1.
Cell biology
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Cell biology is a branch of biology that studies the different structures and functions of the cell and focuses mainly on the idea of the cell as the basic unit of life. This is done both on a microscopic and molecular level as it encompasses prokaryotic cells and eukaryotic cells, knowing the components of cells and how cells work is fundamental to all biological sciences, it is also essential for research in bio-medical fields such as cancer, and other diseases. Research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology. The study of the cell is done on a level, however, most of the processes within the cell are made up of a mixture of small organic molecules, inorganic ions, hormones. Approximately 75-85% of the volume is due to water making it an indispensable solvent as a result of its polarity. These molecules within the cell, which operate as substrates, provide an environment for the cell to carry out metabolic reactions. The cell shape varies among the different types of organisms, and are then classified into two categories, eukaryotes and prokaryotes. Cell biology focuses more on the study of cells, and their signalling pathways. This environment of the cell is made up of hydrophilic and hydrophobic regions which allows for the exchange of the above-mentioned molecules and ions. The hydrophilic regions of the cell are mainly on the inside and outside of the cell, the cell membrane consists of lipids and proteins which accounts for its hydrophobicity as a result of being non-polar substances. Therefore, in order for these molecules to participate in reactions, within the cell and they accomplish this process of gaining access to the cell via, osmotic pressure, diffusion, concentration gradients, and membrane channels. Inside of the cell are extensive internal sub-cellular membrane-bounded compartments called organelles, cytoplasm - contents of the main fluid-filled space inside cells, chemical reactions also happen in this jelly-like substance. Nuclear Architecture is important for dictating nuclear function, vacuole - contain cell sap or other storage material. Vesicle - small membrane-bounded spheres inside cells which transport substances, the growth process of the cell does not refer to the size of the cell, but instead the density of the number of cells present in the organism at a given time. Cell growth pertains to the increase in the number of cells present in an organism as it grows and develops, Cells are the foundation of all organisms, they are the fundamental unit of life. The growth and development of the cell are essential for the maintenance of the host, for this process the cell goes through the steps of the cell cycle and development which involves cell growth, DNA replication, cell division, regeneration, specialization, and cell death. The cell cycle is divided into four phases, G1, S, G2. The G phases – which is the growth phase - makes up approximately 95% of the cycle
2.
Plant cell
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Plant cells are eukaryotic cells that differ in several key aspects from the cells of other eukaryotic organisms. A cell wall composed of cellulose and hemicelluloses, pectin and in many cases lignin, is secreted by the protoplast on the outside of the cell membrane. This contrasts with the walls of fungi, which are made of chitin, and of bacteria. Other types of plastids are the amyloplasts, specialized for storage, elaioplasts specialized for fat storage. Parenchyma cells are living cells that have functions ranging from storage and support to photosynthesis, apart from the xylem and phloem in their vascular bundles, leaves are composed mainly of parenchyma cells. Parenchyma cells that contain many chloroplasts and are concerned primarily with photosynthesis are called chlorenchyma cells, others, such as the majority of the parenchyma cells in potato tubers and the seed cotyledons of legumes, have a storage function. Collenchyma cells – collenchyma cells are alive at maturity and have only a primary wall and these cells mature from meristem derivatives that initially resemble parenchyma, but differences quickly become apparent. Plastids do not develop, and the secretory apparatus proliferates to secrete additional primary wall, pectin and hemicellulose are the dominant constituents of collenchyma cell walls of dicotyledon angiosperms, which may contain as little as 20% of cellulose in Petasites. Collenchyma cells are quite elongated, and may divide transversely to give a septate appearance. The role of cell type is to support the plant in axes still growing in length. Stretchable support is a way to describe what collenchyma does. Parts of the strings in celery are collenchyma, Sclerenchyma cells – Sclerenchyma cells are hard and tough cells with a function in mechanical support. They are of two broad types – sclereids or stone cells and fibres, the cells develop an extensive secondary cell wall that is laid down on the inside of the primary cell wall. The secondary wall is impregnated with lignin, making it hard, thus, these cells cannot survive for long as they cannot exchange sufficient material to maintain active metabolism. Sclerenchyma cells are dead at functional maturity, and the cytoplasm is missing, leaving an empty central cavity. Functions for sclereid cells include discouraging herbivory, by damaging digestive passages in small insect larval stages, functions of fibres include provision of load-bearing support and tensile strength to the leaves and stems of herbaceous plants. The major classes of cells differentiate from undifferentiated meristematic cells to form the structures of roots, stems, leaves, flowers. Xylem cells are elongated cells with lignified secondary thickening of the cell walls, xylem cells are specialised for conduction of water, and first appeared in plants during their transition to land in the Silurian period more than 425 million years ago
3.
Plasmodesma
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Plasmodesmata are microscopic channels which traverse the cell walls of plant cells and some algal cells, enabling transport and communication between them. Unlike animal cells, almost every plant cell is surrounded by a cell wall. Neighbouring plant cells are separated by a pair of cell walls. Although cell walls are permeable to soluble proteins and other solutes, plasmodesmata enable direct, regulated. There are two forms of plasmodesmata, primary plasmodesmata, which are formed during cell division, and secondary plasmodesmata, similar structures, called gap junctions and membrane nanotubes, interconnect animal cells and stromules form between plastids in plant cells. Here the wall is not thickened further, and depressions or thin areas known as pits are formed in the walls, pits normally pair up between adjacent cells. Plasmodesmata are approximately 50-60 nm in diameter at the midpoint and are constructed of three layers, the plasma membrane, the cytoplasmic sleeve, and the desmotubule. They can transverse cell walls that are up to 90 nm thick, the plasma membrane portion of the plasmodesma is a continuous extension of the cell membrane or plasmalemma and has a similar phospholipid bilayer structure. The cytoplasmic sleeve is a fluid-filled space enclosed by the plasmalemma and is a extension of the cytosol. Trafficking of molecules and ions through plasmodesmata occurs through this space, smaller molecules and ions can easily pass through plasmodesmata by diffusion without the need for additional chemical energy. Larger molecules, including proteins and RNA, can pass through the cytoplasmic sleeve diffusively. Plasmodesmatal transport of larger molecules is facilitated by mechanisms that are currently unknown. The desmotubule is a tube of appressed endoplasmic reticulum that runs between two adjacent cells, some molecules are known to be transported through this channel, but it is not thought to be the main route for plasmodesmatal transport. These structures may be composed of myosin and actin, which are part of the cells cytoskeleton, if this is the case these proteins could be used in the selective transport of large molecules between the two cells. Plasmodesmata have been shown to transport proteins, short interfering RNA, messenger RNA, viroids, one example of a viral movement proteins is the tobacco mosaic virus MP-30. MP-30 is thought to bind to the viruss own genome and shuttle it from infected cells to uninfected cells through plasmodesmata, flowering Locus T protein moves from leaves to the shoot apical meristem through plasmodesmata to initiate flowering. Plasmodesmata are also used by cells in phloem, and symplastic transport is used to regulate the cells by the companion cells. The size of molecules that can pass through plasmodesmata is determined by the exclusion limit
4.
Cell membrane
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The cell membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is permeable to ions and organic molecules and controls the movement of substances in. The basic function of the membrane is to protect the cell from its surroundings. It consists of the bilayer with embedded proteins. Cell membranes can be artificially reassembled, Some authors that did not believe that there was a functional permeable boundary at the surface of the cell preferred to use the term plasmalemma to the extern region of the cell. The cell membrane surrounds the cytoplasm of living cells, physically separating the components from the extracellular environment. The cell membrane also plays a role in anchoring the cytoskeleton to provide shape to the cell, fungi, bacteria, most archaea, and plants also have a cell wall, which provides a mechanical support to the cell and precludes the passage of larger molecules. The cell membrane is permeable and able to regulate what enters and exits the cell. The movement of substances across the membrane can be passive, occurring without the input of cellular energy, or active. The membrane also maintains the cell potential, the cell membrane thus works as a selective filter that allows only certain things to come inside or go outside the cell. The cell employs a number of mechanisms that involve biological membranes,1. Passive osmosis and diffusion, Some substances such as carbon dioxide and oxygen, can move across the membrane by diffusion. Because the membrane acts as a barrier for certain molecules and ions, such a concentration gradient across a semipermeable membrane sets up an osmotic flow for the water. Transmembrane protein channels and transporters, Nutrients, such as sugars or amino acids, must enter the cell, such molecules diffuse passively through protein channels such as aquaporins in facilitated diffusion or are pumped across the membrane by transmembrane transporters. Protein channel proteins, also called permeases, are quite specific, recognizing and transporting only a limited food group of chemical substances. Endocytosis, Endocytosis is the process in which cells absorb molecules by engulfing them, the plasma membrane creates a small deformation inward, called an invagination, in which the substance to be transported is captured. The deformation then pinches off from the membrane on the inside of the cell, Endocytosis is a pathway for internalizing solid particles, small molecules and ions, and macromolecules. Endocytosis requires energy and is thus a form of active transport and this is the process of exocytosis
5.
Chloroplast
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Chloroplasts /ˈklɔːrəˌplæsts, -plɑːsts/ are organelles, specialized subunits, in plant and algal cells. Their discovery inside plant cells is usually credited to Julius von Sachs and they then use the ATP and NADPH to make organic molecules from carbon dioxide in a process known as the Calvin cycle. Chloroplasts carry out a number of functions, including fatty acid synthesis, much amino acid synthesis. The number of chloroplasts per cell varies from one, in algae, up to 100 in plants like Arabidopsis. A chloroplast is a type of known as a plastid. Other plastid types, such as the leucoplast and the chromoplast, contain little chlorophyll, chloroplasts are highly dynamic—they circulate and are moved around within plant cells, and occasionally pinch in two to reproduce. Their behavior is influenced by environmental factors like light color. Chloroplasts, like mitochondria, contain their own DNA, which is thought to be inherited from their ancestor—a photosynthetic cyanobacterium that was engulfed by a eukaryotic cell. Chloroplasts cannot be made by the plant cell and must be inherited by each cell during cell division. With one exception, all chloroplasts can probably be traced back to a single endosymbiotic event, despite this, chloroplasts can be found in an extremely wide set of organisms, some not even directly related to each other—a consequence of many secondary and even tertiary endosymbiotic events. The word chloroplast is derived from the Greek words chloros, which means green, and plastes, the first definitive description of a chloroplast was given by Hugo von Mohl in 1837 as discrete bodies within the green plant cell. In 1883, A. F. W. Schimper would name these bodies as chloroplastids, in 1884, Eduard Strasburger adopted the term chloroplasts. Chloroplasts are one of many types of organelles in the plant cell and they are considered to have originated from cyanobacteria through endosymbiosis—when a eukaryotic cell engulfed a photosynthesizing cyanobacterium that became a permanent resident in the cell. Mitochondria are thought to have come from an event, where an aerobic prokaryote was engulfed. This origin of chloroplasts was first suggested by the Russian biologist Konstantin Mereschkowski in 1905 after Andreas Schimper observed in 1883 that chloroplasts closely resemble cyanobacteria, chloroplasts are only found in plants, algae, and the amoeboid Paulinella chromatophora. Cyanobacteria are considered the ancestors of chloroplasts and they are sometimes called blue-green algae even though they are prokaryotes. They are a phylum of bacteria capable of carrying out photosynthesis. Cyanobacteria also contain a cell wall, which is thicker than in other gram-negative bacteria
6.
Thylakoid
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A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacteria. They are the site of the light-dependent reactions of photosynthesis, thylakoids consist of a thylakoid membrane surrounding a thylakoid lumen. Chloroplast thylakoids frequently form stacks of disks referred to as grana, grana are connected by intergranal or stroma thylakoids, which join granum stacks together as a single functional compartment. The word thylakoid comes from the Greek word thylakos meaning sac or pouch, thus, thylakoid means sac-like or pouch-like. Thylakoids are membrane-bound structures embedded in the chloroplast stroma, a stack of thylakoids is called a granum and resembles a stack of coins. The thylakoid membrane is the site of the light-dependent reactions of photosynthesis with the photosynthetic pigments embedded directly in the membrane and it is an alternating pattern of dark and light bands measuring each 1 nanometre. The thylakoid lipid bilayer shares characteristic features with prokaryotic membranes and the inner chloroplast membrane, for example, acidic lipids can be found in thylakoid membranes, cyanobacteria and other photosynthetic bacteria and are involved in the functional integrity of the photosystems. The thylakoid membranes of plants are composed primarily of phospholipids and galactolipids that are asymmetrically arranged along. Thylakoid membranes are richer in galactolipids rather than phospholipids, also they predominantly consist of hexagonal phase II forming monogalacotosyl diglyceride lipid, despite this unique composition, plant thylakoid membranes have been shown to assume largely lipid-bilayer dynamic organization. The thylakoid lumen is an aqueous phase enclosed by the thylakoid membrane. It plays an important role for photophosphorylation during photosynthesis, during the light-dependent reaction, protons are pumped across the thylakoid membrane into the lumen making it acidic down to pH4. In higher plants thylakoids are organized into a granum-stroma membrane assembly, a granum is a stack of thylakoid discs. Chloroplasts can have from 10 to 100 grana, grana are connected by stroma thylakoids, also called intergranal thylakoids or lamellae. Grana thylakoids and stroma thylakoids can be distinguished by their different protein composition, grana contribute to chloroplasts large surface area to volume ratio. Different interpretations of electron tomography imaging of thylakoid membranes has resulted in two models for grana structure, chloroplasts develop from proplastids when seedlings emerge from the ground. In the plant embryo and in the absence of light, proplastids develop into etioplasts that contain semicrystalline membrane structures called prolamellar bodies, when exposed to light, these prolamellar bodies develop into thylakoids. This does not happen in seedlings grown in the dark, which undergo etiolation, an underexposure to light can cause the thylakoids to fail. This causes the chloroplasts to fail resulting in the death of the plant, thylakoid formation requires the action of vesicle-inducing protein in plastids 1
7.
Vacuole
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A vacuole is a membrane-bound organelle which is present in all plant and fungal cells and some protist, animal and bacterial cells. Vacuoles are formed by the fusion of multiple membrane vesicles and are effectively just larger forms of these, the organelle has no basic shape or size, its structure varies according to the needs of the cell. In seeds, stored proteins needed for germination are kept in protein bodies, vacuoles also play a major role in autophagy, maintaining a balance between biogenesis and degradation, of many substances and cell structures in certain organisms. They also aid in the lysis and recycling of misfolded proteins that have begun to build up within the cell, thomas Boller and others proposed that the vacuole participates in the destruction of invading bacteria and Robert B Mellor proposed organ-specific forms have a role in housing symbiotic bacteria. In protists, vacuoles have the function of storing food which has been absorbed by the organism and assisting in the digestive. The vacuole probably evolved several times independently, even within the Viridiplantae, contractile vacuoles were first observed by Spallanzani in protozoa, although mistaken for respiratory organs. Dujardin named these stars as vacuoles, in 1842, Schleiden applied the term for plant cells, to distinguish the structure with cell sap from the rest of the protoplasm. In 1885, de Vries named the vacuoule membrane as tonoplast, large vacuoles are found in three genera of filamentous sulfur bacteria, the Thioploca, Beggiatoa and Thiomargarita. The cytosol is extremely reduced in these genera and the vacuole can occupy between 40–98% of the cell, the vacuole contains high concentrations of nitrate ions and is therefore thought to be a storage organelle. Gas vacuoles, which are freely permeable to gas, are present in species of Cyanobacteria. They allow the bacteria to control their buoyancy, most mature plant cells have one large vacuole that typically occupies more than 30% of the cells volume, and that can occupy as much as 80% of the volume for certain cell types and conditions. Strands of cytoplasm often run through the vacuole, a vacuole is surrounded by a membrane called the tonoplast and filled with cell sap. Also called the membrane, the tonoplast is the cytoplasmic membrane surrounding a vacuole. As a membrane, it is involved in regulating the movements of ions around the cell. The low pH of the vacuole also allows degradative enzymes to act, although single large vacuoles are most common, the size and number of vacuoles may vary in different tissues and stages of development. For example, developing cells in the meristems contain small provacuoles and cells of the vascular cambium have many small vacuoles in the winter, aside from storage, the main role of the central vacuole is to maintain turgor pressure against the cell wall. Proteins found in the tonoplast control the flow of water into and out of the vacuole through active transport, pumping potassium ions into, due to osmosis, water will diffuse into the vacuole, placing pressure on the cell wall. If water loss leads to a significant decline in turgor pressure, turgor pressure exerted by the vacuole is also essential in supporting plants in an upright position
8.
Mitochondrion
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The mitochondrion is a double membrane-bound organelle found in all eukaryotic organisms. Some cells in multicellular organisms may however lack them. A number of organisms, such as microsporidia, parabasalids. To date, only one eukaryote, Monocercomonoides, is known to have completely lost its mitochondria, the word mitochondrion comes from the Greek μίτος, mitos, thread, and χονδρίον, chondrion, granule or grain-like. Mitochondria generate most of the supply of adenosine triphosphate, used as a source of chemical energy. Mitochondria are commonly between 0.75 and 3 μm in diameter but vary considerably in size and structure, unless specifically stained, they are not visible. Mitochondrial biogenesis is in turn temporally coordinated with these cellular processes, Mitochondria have been implicated in several human diseases, including mitochondrial disorders, cardiac dysfunction, heart failure and autism. The number of mitochondria in a cell can vary widely by organism, tissue, for instance, red blood cells have no mitochondria, whereas liver cells can have more than 2000, The organelle is composed of compartments that carry out specialized functions. These compartments or regions include the outer membrane, the space, the inner membrane. Although most of a cells DNA is contained in the cell nucleus, mitochondrial proteins vary depending on the tissue and the species. In humans,615 distinct types of protein have been identified from cardiac mitochondria, the mitochondrial proteome is thought to be dynamically regulated. The first observations of structures that probably represented mitochondria were published in the 1840s. Richard Altmann, in 1890, established them as cell organelles, the term mitochondria was coined by Carl Benda in 1898. Leonor Michaelis discovered that Janus green can be used as a stain for mitochondria in 1900. Benjamin F. Kingsbury, in 1912, first related them with cell respiration, in 1913, particles from extracts of guinea-pig liver were linked to respiration by Otto Heinrich Warburg, which he called grana. Warburg and Heinrich Otto Wieland, who had postulated a similar particle mechanism. It was not until 1925, when David Keilin discovered cytochromes, in the following years, the mechanism behind cellular respiration was further elaborated, although its link to the mitochondria was not known. The introduction of tissue fractionation by Albert Claude allowed mitochondria to be isolated from other cell fractions, in 1946, he concluded that cytochrome oxidase and other enzymes responsible for the respiratory chain were isolated to the mitchondria
9.
Peroxisome
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Peroxisomes IPA, are organelles found in virtually all eukaryotic cells. e. Ether phospholipids critical for the function of mammalian brains and lungs. They also contain approximately 10% of the activity of two enzymes in the pentose phosphate pathway, which is important for energy metabolism. It is vigorously debated if peroxisomes are involved in isoprenoid and cholesterol synthesis in animals, peroxisomes were identified as organelles by the Belgian cytologist Christian de Duve in 1967 after they had been first described by a Swedish doctoral student, J. Rhodin in 1954. A major function of the peroxisome is the breakdown of very long fatty acids through beta-oxidation. In animal cells, the fatty acids are converted to medium chain fatty acids. In yeast and plant cells, this process is carried out exclusively in peroxisomes, the first reactions in the formation of plasmalogen in animal cells also occur in peroxisomes. Plasmalogen is the most abundant phospholipid in myelin, deficiency of plasmalogens causes profound abnormalities in the myelination of nerve cells, which is one reason why many peroxisomal disorders affect the nervous system. Peroxisomes contain oxidative enzymes, such as D-amino acid oxidase and uric acid oxidase, however the last enzyme is absent in humans, explaining the disease known as gout, caused by the accumulation of uric acid. This reaction is important in liver and kidney cells, where the peroxisomes detoxify various toxic substances that enter the blood, about 25% of the ethanol alcohol humans drink is oxidized to acetaldehyde in this way. Dismutase, the components of the cycle, and the NADP-dehydrogenases of the pentose-phosphate pathway. It has been demonstrated that peroxisomes generate superoxide and nitric oxide radicals, the peroxisome of plant cells is polarised when fighting fungal penetration. Infection causes a molecule to play an antifungal role to be made. Peroxisomes can be derived from the reticulum and replicate by fission. Peroxisome matrix proteins are translated in the prior to import. Specific amino acid sequences at the C-terminus or N-terminus of peroxisomal matrix proteins signals them to be imported into the organelle, there are at least 32 known peroxisomal proteins, called peroxins, which participate in the process of peroxisome assembly. Proteins do not have to unfold to be imported into the peroxisome, the protein receptors, the peroxins PEX5 and PEX7, accompany their cargoes all the way into the peroxisome where they release the cargo and then return to the cytosol – a step named recycling. A model describing the import cycle is referred to as the extended shuttle mechanism, there is now evidence that ATP hydrolysis is required for the recycling of receptors to the cytosol
10.
Cytoplasm
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In cell biology, the cytoplasm is the material within a living cell, excluding the cell nucleus. It comprises cytosol and the organelles – the cells internal sub-structures, all of the contents of the cells of prokaryotic organisms are contained within the cytoplasm. Within the cells of organisms the contents of the cell nucleus are separated from the cytoplasm. The cytoplasm is about 80% water and usually colorless, the submicroscopic ground cell substance or cytoplasmatic matrix which remains after exclusion the cell organelles and particles is groundplasm. It is within the cytoplasm that most cellular activities occur, such as many metabolic pathways including glycolysis, the concentrated inner area is called the endoplasm and the outer layer is called the cell cortex or the ectoplasm. Movement of calcium ions in and out of the cytoplasm is an activity for metabolic processes. In plants, movement of the cytoplasm around vacuoles is known as cytoplasmic streaming, the term was introduced by Rudolf von Kölliker in 1863, originally as a synonym for protoplasm, but later it has come to mean the cell substance and organelles outside the nucleus. There has been disagreement on the definition of cytoplasm, as some authors prefer to exclude from it some organelles. The physical properties of the cytoplasm have been contested in recent years and it remains uncertain how the varied components of the cytoplasm interact to allow movement of particles and organelles while maintaining the cell’s structure. The flow of cytoplasmic components plays an important role in cellular functions which are dependent on the permeability of the cytoplasm. An example of function is cell signalling, a process which is dependent on the manner in which signaling molecules are allowed to diffuse across the cell. While small signaling molecules like calcium ions are able to diffuse with ease, larger molecules, the irregular dynamics of such particles have given rise to various theories on the nature of the cytoplasm. There has long been evidence that the cytoplasm behaves like a sol-gel and it is thought that the component molecules and structures of the cytoplasm behave at times like a disordered colloidal solution and at other times like an integrated network, forming a solid mass. Recently it has proposed that the cytoplasm behaves like a glass-forming liquid approaching the glass transition. A cells ability to vitrify in the absence of activity, as in dormant periods. There has been examining the motion of cytoplasmic particles independent of the nature of the cytoplasm. In such an approach, the aggregate random forces within the cell caused by motor proteins explain the non-Brownian motion of cytoplasmic constituents. The three major elements of the cytoplasm are the cytosol, organelles and inclusions, the cytosol is the portion of the cytoplasm not contained within membrane-bound organelles
11.
Endoplasmic reticulum
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The endoplasmic reticulum is a type of organelle in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the nuclear membrane. The endoplasmic reticulum occurs in most types of cells, including Giardia. There are two types of endoplasmic reticulum, rough and smooth, the outer face of the rough endoplasmic reticulum is studded with ribosomes that are the sites of protein synthesis. The rough endoplasmic reticulum is especially prominent in such as hepatocytes. The smooth endoplasmic reticulum lacks ribosomes and functions in lipid manufacture and metabolism, the production of steroid hormones, the smooth ER is especially abundant in mammalian liver and gonad cells. The lacy membranes of the endoplasmic reticulum were first seen in 1945 using electron microscopy, the lacy membranes of the endoplasmic reticulum were first seen in 1945 by Keith R. Porter, Albert Claude, Brody Meskers and Ernest F. Fullam, using electron microscopy. The word reticulum, which network, was applied to describe this fabric of membranes. The general structure of the reticulum is a network of membranes called cisternae. These sac-like structures are held together by the cytoskeleton, the phospholipid membrane encloses the cisternal space, which is continuous with the perinuclear space but separate from the cytosol. The functions of the reticulum can be summarized as the synthesis and export of proteins and membrane lipids. The quantity of both rough and smooth endoplasmic reticulum in a cell can slowly interchange from one type to the other, transformation can include embedding of new proteins in membrane as well as structural changes. Changes in protein content may occur without noticeable structural changes, the surface of the rough endoplasmic reticulum is studded with protein-manufacturing ribosomes giving it a rough appearance. The binding site of the ribosome on the endoplasmic reticulum is the translocon. However, the ribosomes are not a part of this organelles structure as they are constantly being bound. A ribosome only binds to the RER once a specific protein-nucleic acid complex forms in the cytosol and this special complex forms when a free ribosome begins translating the mRNA of a protein destined for the secretory pathway. The first 5-30 amino acids polymerized encode a signal peptide, a message that is recognized. Translation pauses and the complex binds to the RER translocon where translation continues with the nascent protein forming into the RER lumen and/or membrane
12.
Cell nucleus
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In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. Eukaryotes usually have a nucleus, but a few cell types, such as mammalian red blood cells, have no nuclei. Cell nuclei contain most of the genetic material, organized as multiple long linear DNA molecules in complex with a large variety of proteins, such as histones. The genes within these chromosomes are the nuclear genome and are structured in such a way to promote cell function. The nucleus maintains the integrity of genes and controls the activities of the cell by regulating gene expression—the nucleus is, therefore, because the nuclear membrane is impermeable to large molecules, nuclear pores are required to regulate nuclear transport of molecules across the envelope. The pores cross both nuclear membranes, providing a channel through which larger molecules must be transported by carrier proteins while allowing free movement of small molecules. Movement of large molecules such as proteins and RNA through the pores is required for gene expression and the maintenance of chromosomes. The best-known of these is the nucleolus, which is involved in the assembly of ribosomes. After being produced in the nucleolus, ribosomes are exported to the cytoplasm where they translate mRNA, the nucleus was the first organelle to be discovered. What is most likely the oldest preserved drawing dates back to the early microscopist Antonie van Leeuwenhoek and he observed a lumen, the nucleus, in the red blood cells of salmon. Unlike mammalian red blood cells, those of other vertebrates still contain nuclei, the nucleus was also described by Franz Bauer in 1804 and in more detail in 1831 by Scottish botanist Robert Brown in a talk at the Linnean Society of London. Brown was studying orchids under microscope when he observed an opaque area and he did not suggest a potential function. In 1838, Matthias Schleiden proposed that the plays a role in generating cells. He believed that he had observed new cells assembling around cytoblasts, Franz Meyen was a strong opponent of this view, having already described cells multiplying by division and believing that many cells would have no nuclei. The function of the nucleus remained unclear, between 1877 and 1878, Oscar Hertwig published several studies on the fertilization of sea urchin eggs, showing that the nucleus of the sperm enters the oocyte and fuses with its nucleus. This was the first time it was suggested that an individual develops from a nucleated cell, therefore, the necessity of the sperm nucleus for fertilization was discussed for quite some time. However, Hertwig confirmed his observation in other groups, including amphibians. Eduard Strasburger produced the results for plants in 1884
13.
Nuclear pore
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Nuclear pores are large protein complexes that cross the nuclear envelope, which is the double membrane surrounding the eukaryotic cell nucleus. There are about an average of 2000 nuclear pore complexes, in the envelope of a vertebrate cell, but it varies depending on cell type. The proteins that make up the pore complex are known as nucleoporins. About half of the nucleoporins typically contain solenoid protein domains—either an alpha solenoid or a beta-propeller fold, each NPC contains at least 456 individual protein molecules and is composed of 30 distinct proteins. The other half show structural characteristics typical of natively unfolded or intrinsically disordered proteins and these disordered proteins are the FG nucleoporins, so called because their amino-acid sequence contains many phenylalanine—glycine repeats. Nuclear pore complexes allow the transport of molecules across the nuclear envelope and this transport includes RNA and ribosomal proteins moving from nucleus to the cytoplasm and proteins, carbohydrates, signaling molecules and lipids moving into the nucleus. It is notable that the pore complex can actively conduct 1000 translocations per complex per second. Nucleoporin-mediated transport is not directly energy requiring, but depends on concentrations gradients associated with the RAN cycle, each of the eight protein subunits surrounding the actual pore projects a spoke-shaped protein over the pore channel. The center of the pore often appears to contain a plug-like structure and it is yet unknown whether this corresponds to an actual plug or is merely cargo caught in transit. The entire nuclear pore complex has a diameter of about 120 nanometers in vertebrates, the molecular mass of the mammalian NPC is about 124 megadaltons and it contains approximately 30 different protein components, each in multiple copies. In contrast, the yeast Saccharomyces cerevisiae is smaller, weighing only 66 MDa, small particles are able to pass through the nuclear pore complex by passive diffusion. Larger particles are able to diffuse passively through the large diameter of the pore. Other nuclar transport receptors include NTF2 and some NTF2-like proteins, several NLS sequences are known, generally containing a conserved sequence with basic residues such as PKKKRKV. Any material with an NLS will be taken up by importins to the nucleus, the classical scheme of NLS-protein importation begins with Importin-α first binding to the NLS sequence, which then acts as a bridge for Importin-β to attach. The importinβ—importinα—cargo complex is directed towards the nuclear pore and diffuses through it. Once the complex is in the nucleus, RanGTP binds to Importin-β, then the cellular apoptosis susceptibility protein, an exportin which in the nucleus is bound to RanGTP, displaces Importin-α from the cargo. The NLS-protein is thus free in the nucleoplasm, although cargo passes through the pore with the assistance of chaperone proteins, the translocation through the pore itself is not energy-dependent. However, the import cycle needs the hydrolysis of 2 GTPs and is thus energy-dependent and has to be considered as active transport
14.
Nuclear membrane
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A nuclear membrane, also known as the nucleolemma or karyotheca, is the phospho lipid bilayer membrane which surrounds the genetic material and nucleolus in eukaryotic cells. The nuclear membrane consists of two lipid bilayers—the inner nuclear membrane, and the nuclear membrane. The space between the membranes is called the space, a region contiguous with the lumen of the endoplasmic reticulum. It is usually about 20–40 nm wide, the nuclear membrane also has many small holes called nuclear pores that allow material to move in and out of the nucleus. The outer nuclear membrane also shares a border with the endoplasmic reticulum. While it is linked, the outer nuclear membrane contains proteins found in far higher concentrations than the endoplasmic reticulum. All 4 Nesprin proteins present in mammals are expressed in the nuclear membrane. Nesprin proteins connect cytoskeletal filaments to the nucleoskeleton, nesprin-mediated connections to the cytoskeleton contribute to nuclear positioning and to the cell’s mechanosensory function. Nesprin-3 and-4 may play a role in unloading cargo, Nesprin-3 proteins bind plectin. Nesprin-4 proteins bind the end directed motor kinesin-1. The outer nuclear membrane is also involved in development, as it fuses with the nuclear membrane to form nuclear pores. It is connected to the membrane by nuclear pores which penetrate the membranes. While the two membranes and the reticulum are linked, proteins embedded in the membranes tend to stay put rather than dispersing across the continuum. The nuclear membrane is punctured by thousands of nuclear pore complexes—large hollow proteins about 100 nm across and they link the inner and outer nuclear membranes. During the G2 phase of interphase, the membrane increases its surface area. In lower eukaryotes, such as yeast, which undergo closed mitosis, the spindle fibers either form within the membrane, or penetrate it without tearing it apart. In higher eukaryotes, the membrane must break down during the prometaphase state of mitosis to allow the mitotic spindle fibers to access the chromosomes inside. The breakdown and reformation processes are not well understood, in mammals, the nuclear membrane can break down within minutes, following a set of steps during the early stages of Mitosis
15.
Nucleolus
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The nucleolus is the largest structure in the nucleus of eukaryotic cells, where it is primarily responsible for the creation of ribosomes via a process known as ribosome biogenesis. Nucleoli also have important functions like assembly of signal recognition particles. Nucleoli are made of proteins, DNA and RNA and form around specific chromosomal regions, malfunction of nucleoli can be the cause of several human conditions which include diseases, disorders, syndromes and illnesses. Until 1964, little was known about the function of the nucleolus, during that year, a study of nucleoli by John Gurdon and Donald Brown in the African clawed frog Xenopus laevis generated increasing interest in the function and detailed structure of the nucleolus. They found that 25% of the eggs had no nucleolus. Half of the eggs had one nucleolus and 25% had two and they concluded that the nucleolus had a function necessary for life. In 1966 Max L. Birnstiel and Hugh Wallace showed via hybridization experiments that genes within nucleoli code for ribosomal RNA, three major components of the nucleolus are recognized, the fibrillar center, the dense fibrillar component, and the granular component. The DFC consists of newly transcribed rRNA bound to ribosomal proteins, reflecting the substantial increase in the DNA intergenic region, an original fibrillar component would have separated into the FC and the DFC. Another structure identified within many nucleoli is an area in the center of the structure referred to as a nucleolar vacuole. Nucleoli of various plant species have shown to have very high concentrations of iron in contrast to human. Antibodies against the PAF49 protein can also be used as a marker for the nucleolus in immunofluorescence experiments, nucleoli are formed around specific genetic loci called nucleolar organizing regions, first described by Barbara McClintock. Because of this organization, the nucleolus is defined as a genetically determined element. An NOR is composed of repeats of rDNA, which can be found on several different chromosomes. The human genome, for example, contains more than 200 clustered copies of rDNA on five different chromosomes, in a typical eukaryote rDNA consists of a promoter, internal and external transcribed spacers, rRNA coding sequences and an intergenic spacer. In ribosome biogenesis, two of the three eukaryotic RNA polymerases are required, and these function in a coordinated manner, in an initial stage, the rRNA genes are transcribed as a single unit within the nucleolus by RNA polymerase I. In order for transcription to occur, several pol I-associated factors. In yeast, the most important are, UAF, TBP, and CF, which bind promoter elements and form the preinitiation complex, in humans, a similar PIC is assembled with SL1, the promoter selectivity factor, transcription initiation factors, and UBF. RNA polymerase I transcribes most rRNA transcripts but the 5S rRNA subunit is transcribed by RNA polymerase III, transcription of rRNA yields a long precursor molecule which still contains the ITS and ETS
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Ribosome
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The ribosome is a complex molecular machine, found within all living cells, that serves as the site of biological protein synthesis. Ribosomes link amino acids together in the order specified by messenger RNA molecules, ribosomes consist of two major components, the small ribosomal subunit, which reads the RNA, and the large subunit, which joins amino acids to form a polypeptide chain. Each subunit is composed of one or more ribosomal RNA molecules, the ribosomes and associated molecules are also known as the translational apparatus. The sequence of DNA, which encodes the sequence of the acids in a protein, is copied into a messenger RNA chain. It may be copied many times into RNA chains, ribosomes can bind to a messenger RNA chain and use its sequence for determining the correct sequence of amino acids. Amino acids are selected, collected, and carried to the ribosome by transfer RNA molecules and it is during this binding that the correct translation of nucleic acid sequence to amino acid sequence occurs. For each coding triplet in the messenger RNA there is a distinct transfer RNA that matches, the attached amino acids are then linked together by another part of the ribosome. Once the protein is produced, it can then fold to produce a specific functional three-dimensional structure although during synthesis some proteins start folding into their correct form, a ribosome is made from complexes of RNAs and proteins and is therefore a ribonucleoprotein. When a ribosome finishes reading an mRNA molecule, these two subunits split apart, ribosomes are ribozymes, because the catalytic peptidyl transferase activity that links amino acids together is performed by the ribosomal RNA. Ribosomes are often associated with the membranes that make up the rough endoplasmic reticulum. Ribosomes from bacteria, archaea and eukaryotes in the system, resemble each other to a remarkable degree. They differ in their size, sequence, structure, and the ratio of protein to RNA, the differences in structure allow some antibiotics to kill bacteria by inhibiting their ribosomes, while leaving human ribosomes unaffected. In bacteria and archaea, more than one ribosome may move along a single mRNA chain at one time, each reading its sequence, ribosomes were first observed in the mid-1950s by Romanian cell biologist George Emil Palade, using an electron microscope, as dense particles or granules. The Nobel Prize in Chemistry 2009 was awarded to Venkatraman Ramakrishnan, Thomas A. Steitz and Ada E. Yonath for determining the detailed structure, the ribosome is a highly complex cellular machine. It is largely made up of specialized RNA known as ribosomal RNA as well as dozens of distinct proteins, the ribosomal proteins and rRNAs are arranged into two distinct ribosomal pieces of different size, known generally as the large and small subunit of the ribosome. Ribosomes consist of two subunits that fit together and work as one to translate the mRNA into a polypeptide chain during protein synthesis, because they are formed from two subunits of non-equal size, they are slightly longer in the axis than in diameter. Prokaryotic ribosomes are around 20 nm in diameter and are composed of 65% rRNA, eukaryotic ribosomes are between 25 and 30 nm in diameter with an rRNA-to-protein ratio that is close to 1. Bacterial ribosomes are composed of one or two rRNA strands, eukaryotic ribosomes contain one or three very large rRNA molecules and multiple smaller protein molecules
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Golgi apparatus
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The Golgi apparatus, also known as the Golgi complex, Golgi body, or simply the Golgi, is an organelle found in most eukaryotic cells. It was identified in 1897 by the Italian scientist Camillo Golgi, part of the cellular endomembrane system, the Golgi apparatus packages proteins into membrane-bound vesicles inside the cell before the vesicles are sent to their destination. The Golgi apparatus resides at the intersection of the secretory, lysosomal, owing to its large size and distinctive structure, the Golgi apparatus was one of the first organelles to be discovered and observed in detail. It was discovered in 1898 by Italian physician Camillo Golgi during an investigation of the nervous system, after first observing it under his microscope, he termed the structure the internal reticular apparatus. Some doubted the discovery at first, arguing that the appearance of the structure was merely an illusion created by the observation technique used by Golgi. With the development of modern microscopes in the 20th century, the discovery was confirmed, early references to the Golgi referred to it by various names including the Golgi–Holmgren apparatus, Golgi–Holmgren ducts, and Golgi–Kopsch apparatus. The term Golgi apparatus was used in 1910 and first appeared in the literature in 1913. Among eukaryotes, the localization of the Golgi apparatus differs. In mammals, a single Golgi apparatus complex is located near the cell nucleus. Tubular connections are responsible for linking the stacks together, localization and tubular connections of the Golgi apparatus are dependent on microtubules. If microtubules are experimentally depolymerized, then the Golgi apparatus loses connections, in yeast, multiple Golgi apparatuses are scattered throughout the cytoplasm. In plants, Golgi stacks are not concentrated at the centrosomal region, organization of the plant Golgi depends on actin cables and not microtubules. The common feature among Golgi is that they are adjacent to endoplasmic reticulum exit sites, in most eukaryotes, the Golgi apparatus is made up of a series of compartments consisting of two main networks, the cis Golgi network and the trans Golgi network. The CGN is a collection of fused, flattened membrane-enclosed disks known as cisternae, a mammalian cell typically contains 40 to 100 stacks. Between four and eight cisternae are usually present in a stack, however and this collection of cisternae is broken down into cis, medial, and trans compartments. The TGN is the final structure, from which proteins are packaged into vesicles destined to lysosomes, secretory vesicles. The TGN is usually positioned adjacent to the stacks of the Golgi apparatus, the TGN may act as an early endosome in yeast and plants. There are structural and organizational differences in the Golgi apparatus among eukaryotes, in some yeasts, Golgi stacking is not observed
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Cytoskeleton
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A cytoskeleton is present in all cells of all domains of life. It is a network of interlinking filaments and tubules that extend throughout the cytoplasm. The cytoskeletal systems of different organisms are composed of similar proteins, the structure, function and dynamic behaviour of the cytoskeleton can be very different, depending on organism and cell type. Even within one cell the cytoskeleton can change through association with other proteins, there is a multitude of functions that the cytoskeleton can perform. Primarily, it gives the cell its shape and mechanical resistance to deformation, the cytoskeleton can also actively contract, thereby deforming the cell and the cells environment and allowing cells to migrate. Furthermore, it forms specialized structures, such as flagella, cilia, lamellipodia, a large-scale example of an action performed by the cytoskeleton is muscle contraction. During contraction of a muscle, within each cell, myosin molecular motors collectively exert forces on parallel actin filaments. This action contracts the muscle cell, and through the process in many muscle cells. In 1903, Nikolai K. Koltsov proposed that the shape of cells was determined by a network of tubules that he termed the cytoskeleton, eukaryotic cells contain three main kinds of cytoskeletal filaments, microfilaments, microtubules, and intermediate filaments. Each cytoskeletal filament has a shape and intracellular distribution, additionally, the filaments are formed by polymerization of different types of sub-units. The microfilament consist of the polymers of the protein actin which has a diameter of 7 nm, the microtubules are made up of the protein called tubulin which has a diameter of 25 nm. Intermediate filaments are made up of proteins which varies depending on the cell type. These type of filament normally have diameters ranging from 8-12 nm, the cytoskeleton provides the cell with structure and shape, and by excluding macromolecules from some of the cytosol, it adds to the level of macromolecular crowding in this compartment. Cytoskeletal elements interact extensively and intimately with cellular membranes, a number of small molecule cytoskeletal drugs have been discovered that interact with actin and microtubules. These compounds have proven useful in studying the cytoskeleton and several have clinical applications, all filaments interact with accessory proteins that regulate and link the filaments to other cell compounds and each other. The accessory proteins are essential for controlled assembly of cytoskeletal filaments in particular locations, microfilaments are composed of linear polymers of G-actin proteins, and generate force when the growing end of the filament pushes against a barrier, such as the cell membrane. They also act as tracks for the movement of molecules that attach to the microfilament. Myosin motoring along F-actin filaments generates contractile forces in so-called actomyosin fibers, actin structures are controlled by the Rho family of small GTP-binding proteins such as Rho itself for contractile acto-myosin filaments, Rac for lamellipodia and Cdc42 for filopodia
19.
Cell (biology)
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The cell is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life that can replicate independently, the study of cells is called cell biology. Cells consist of cytoplasm enclosed within a membrane, which contains many such as proteins. Organisms can be classified as unicellular or multicellular, while the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion cells. Most plant and animal cells are only under a microscope. The cell was discovered by Robert Hooke in 1665, who named the unit for its resemblance to cells inhabited by Christian monks in a monastery. Cells emerged on Earth at least 3.5 billion years ago, Cells are of two types, eukaryotic, which contain a nucleus, and prokaryotic, which do not. Prokaryotes are single-celled organisms, while eukaryotes can be either single-celled or multicellular, prokaryotic cells were the first form of life on Earth, characterised by having vital biological processes including cell signaling and being self-sustaining. They are simpler and smaller than eukaryotic cells, and lack membrane-bound organelles such as the nucleus, prokaryotes include two of the domains of life, bacteria and archaea. The DNA of a prokaryotic cell consists of a chromosome that is in direct contact with the cytoplasm. The nuclear region in the cytoplasm is called the nucleoid, most prokaryotes are the smallest of all organisms ranging from 0.5 to 2.0 µm in diameter. Though most prokaryotes have both a cell membrane and a wall, there are exceptions such as Mycoplasma and Thermoplasma which only possess the cell membrane layer. The envelope gives rigidity to the cell and separates the interior of the cell from its environment, the cell wall consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from expanding and bursting from osmotic pressure due to a hypotonic environment, some eukaryotic cells also have a cell wall. Inside the cell is the region that contains the genome, ribosomes. The genetic material is found in the cytoplasm. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular, linear bacterial plasmids have been identified in several species of spirochete bacteria, including members of the genus Borrelia notably Borrelia burgdorferi, which causes Lyme disease. Though not forming a nucleus, the DNA is condensed in a nucleoid, plasmids encode additional genes, such as antibiotic resistance genes
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Prokaryote
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A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle. The word prokaryote comes from the Greek πρό before and καρυόν nut or kernel, prokaryotes can be divided into two domains, Archaea and bacteria. In contrast, species with nuclei and organelles are placed in the domain Eukaryota, in the prokaryotes, all the intracellular water-soluble components are located together in the cytoplasm enclosed by the cell membrane, rather than in separate cellular compartments. Bacteria, however, do possess protein-based bacterial microcompartments, which are thought to act as primitive organelles enclosed in protein shells, some prokaryotes, such as cyanobacteria may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles, molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species. Eukaryotes are organisms, including humans, whose cells have a well defined membrane-bound nucleus, the division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization. Distinctive types of prokaryotes include extremophiles and methanogens, these are common in extreme environments. Prokaryotes have a cytoskeleton, albeit more primitive than that of the eukaryotes. At least some also contain intracellular structures that can be seen as primitive organelles. Membranous organelles are known in some groups of prokaryotes, such as vacuoles or membrane systems devoted to special metabolic properties, in addition, some species also contain carbohydrate-enclosed microcompartments, which have distinct physiological roles. Most prokaryotes are between 1 µm and 10 µm, but they can vary in size from 0.2 µm to 750 µm, Bacteria and archaea reproduce through asexual reproduction, usually by binary fission. DNA transfer between prokaryotic cells occurs in bacteria and archaea, although it has mainly studied in bacteria. In bacteria, gene transfer occurs by three processes and these are bacterial virus -mediated transduction, plasmid-mediated conjugation, and natural transformation. Transduction of bacterial genes by bacteriophage appears to reflect an occasional error during intracellular assembly of virus particles, the transfer of bacterial DNA is under the control of the bacteriophage’s genes rather than bacterial genes. Conjugation in the well-studied E. coli system is controlled by plasmid genes, infrequently during this process, a plasmid may integrate into the host bacterial chromosome, and subsequently transfer part of the host bacterial DNA to another bacterium. Plasmid mediated transfer of host bacterial DNA also appears to be a process rather than a bacterial adaptation. Natural bacterial transformation involves the transfer of DNA from one bacterium to another through the intervening medium, for a bacterium to bind, take up and recombine donor DNA into its own chromosome, it must first enter a special physiological state called competence. About 40 genes are required in Bacillus subtilis for the development of competence, the length of DNA transferred during B. subtilis transformation can be as much as a third to the whole chromosome
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Mycoplasma
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Mycoplasma is a genus of bacteria that lack a cell wall around their cell membrane. Without a cell wall, they are unaffected by many antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic, Mycoplasma species are the smallest bacterial cells yet discovered, can survive without oxygen, and come in various shapes. For example, M. genitalium is flask-shaped, while M. pneumoniae is more elongated, hundreds of mycoplasma species infect animals. Other species of Mycoplasma other than listed below have been recovered from humans. These use humans as the primary host, Mycoplasma species have been isolated from women with bacterial vaginosis, M. genitalium infection is associated with increased risk of cervicitis, pelvic inflammatory disease, preterm birth and spontaneous abortion, and infertility. Mycoplasmae are associated with respiratory distress syndrome, bronchopulmonary dysplasia. Over 100 species have included in the genus Mycoplasma. Microbes of the class Mollicutes, to which Mycoplasma belongs, are parasites or commensals of humans, animals, the genus Mycoplasma uses vertebrate and arthropod hosts. Dietary nitrogen availability has been shown to alter codon bias and genome evolution in Mycoplasma and Phytoplasma, due to the lack of a rigid cell wall, Mycoplasmataceae can contort into a broad range of shapes, from round to oblong. They therefore cannot be classified as rods or cocci, Mycoplasma species are often found in research laboratories as contaminants in cell culture. Mycoplasmal cell culture contamination occurs due to contamination from individuals or contaminated cell culture medium ingredients, Mycoplasma cells are physically small – less than 1 µm, so are difficult to detect with a conventional microscope. Mycoplasmae may induce cellular changes, including chromosome aberrations, changes in metabolism, severe Mycoplasma infections may destroy a cell line. Detection techniques include DNA Probe, enzyme immunoassays, PCR, plating on sensitive agar, an estimated 11 to 15% of U. S. laboratory cell cultures are contaminated with mycoplasma. A Corning study showed that half of U. S. scientists did not test for Mycoplasma contamination in their cell cultures. The study also stated that, in former Czechoslovakia, 100% of cell cultures that were not routinely tested were contaminated while only 2% of those tested were contaminated. Since the U. S. contamination rate was based on a study of companies that routinely checked for Mycoplasma, european contamination rates are higher and that of other countries are higher still. About 1% of published Gene Expression Omnibus data may have been compromised, several antibiotic-containing formulations of antimycoplasmal reagents have been developed over the years
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Algae
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Algae is an informal term for a large, diverse group of photosynthetic organisms which are not necessarily closely related, and is thus polyphyletic. Included organisms range from unicellular genera, such as Chlorella and the diatoms, to forms, such as the giant kelp. Most are aquatic and autotrophic and lack many of the cell and tissue types, such as stomata, xylem, and phloem. No definition of algae is generally accepted, one definition is that algae have chlorophyll as their primary photosynthetic pigment and lack a sterile covering of cells around their reproductive cells. Some authors exclude all prokaryotes thus do not consider cyanobacteria as algae, Algae constitute a polyphyletic group since they do not include a common ancestor, and although their plastids seem to have a single origin, from cyanobacteria, they were acquired in different ways. Green algae are examples of algae that have primary chloroplasts derived from endosymbiotic cyanobacteria, diatoms and brown algae are examples of algae with secondary chloroplasts derived from an endosymbiotic red alga. Algae exhibit a range of reproductive strategies, from simple asexual cell division to complex forms of sexual reproduction. Algae lack the various structures that characterize land plants, such as the phyllids of bryophytes, rhizoids in nonvascular plants, and the roots, leaves, and other organs found in tracheophytes. Most are phototrophic, although some are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some other heterotrophic organisms, such as the apicomplexans, are derived from cells whose ancestors possessed plastids. Fossilized filamentous algae from the Vindhya basin have been dated back to 1.6 to 1.7 billion years ago, the singular alga is the Latin word for seaweed and retains that meaning in English. Although some speculate that it is related to Latin algēre, be cold, a more likely source is alliga, binding, entwining. The Ancient Greek word for seaweed was φῦκος, which could mean either the seaweed or a red dye derived from it, the Latinization, fūcus, meant primarily the cosmetic rouge. It could be any color, black, red, green, accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name Fucus appears in a number of taxa, most algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and presumably represent reduced endosymbiotic cyanobacteria, however, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three groups of algae. Their lineage relationships are shown in the figure in the upper right, many of these groups contain some members that are no longer photosynthetic
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Plant
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Plants are mainly multicellular, predominantly photosynthetic eukaryotes of the kingdom Plantae. The term is generally limited to the green plants, which form an unranked clade Viridiplantae. This includes the plants, conifers and other gymnosperms, ferns, clubmosses, hornworts, liverworts, mosses and the green algae. Green plants have cell walls containing cellulose and obtain most of their energy from sunlight via photosynthesis by primary chloroplasts and their chloroplasts contain chlorophylls a and b, which gives them their green color. Some plants are parasitic and have lost the ability to produce amounts of chlorophyll or to photosynthesize. Plants are characterized by sexual reproduction and alternation of generations, although reproduction is also common. There are about 300–315 thousand species of plants, of which the great majority, green plants provide most of the worlds molecular oxygen and are the basis of most of Earths ecologies, especially on land. Plants that produce grains, fruits and vegetables form humankinds basic foodstuffs, Plants play many roles in culture. They are used as ornaments and, until recently and in variety, they have served as the source of most medicines. The scientific study of plants is known as botany, a branch of biology, Plants are one of the two groups into which all living things were traditionally divided, the other is animals. The division goes back at least as far as Aristotle, who distinguished between plants, which generally do not move, and animals, which often are mobile to catch their food. Much later, when Linnaeus created the basis of the system of scientific classification. Since then, it has become clear that the plant kingdom as originally defined included several unrelated groups, however, these organisms are still often considered plants, particularly in popular contexts. When the name Plantae or plant is applied to a group of organisms or taxon. The evolutionary history of plants is not yet settled. Those which have been called plants are in bold, the way in which the groups of green algae are combined and named varies considerably between authors. Algae comprise several different groups of organisms which produce energy through photosynthesis, most conspicuous among the algae are the seaweeds, multicellular algae that may roughly resemble land plants, but are classified among the brown, red and green algae. Each of these groups also includes various microscopic and single-celled organisms
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Fungus
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A fungus is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from the other eukaryotic life kingdoms of plants, a characteristic that places fungi in a different kingdom from plants, bacteria and some protists, is chitin in their cell walls. Similar to animals, fungi are heterotrophs, they acquire their food by absorbing dissolved molecules, growth is their means of mobility, except for spores, which may travel through the air or water. Fungi are the principal decomposers in ecological systems and this fungal group is distinct from the structurally similar myxomycetes and oomycetes. The discipline of biology devoted to the study of fungi is known as mycology, in the past, mycology was regarded as a branch of botany, although it is now known fungi are genetically more closely related to animals than to plants. Abundant worldwide, most fungi are inconspicuous because of the size of their structures. Fungi include symbionts of plants, animals, or other fungi and they may become noticeable when fruiting, either as mushrooms or as molds. Fungi perform a role in the decomposition of organic matter and have fundamental roles in nutrient cycling. Since the 1940s, fungi have been used for the production of antibiotics, Fungi are also used as biological pesticides to control weeds, plant diseases and insect pests. Many species produce bioactive compounds called mycotoxins, such as alkaloids and polyketides, the fruiting structures of a few species contain psychotropic compounds and are consumed recreationally or in traditional spiritual ceremonies. Fungi can break down manufactured materials and buildings, and become significant pathogens of humans, losses of crops due to fungal diseases or food spoilage can have a large impact on human food supplies and local economies. The fungus kingdom encompasses a diversity of taxa with varied ecologies, life cycle strategies. However, little is known of the biodiversity of Kingdom Fungi. Advances in molecular genetics have opened the way for DNA analysis to be incorporated into taxonomy, phylogenetic studies published in the last decade have helped reshape the classification within Kingdom Fungi, which is divided into one subkingdom, seven phyla, and ten subphyla. The English word fungus is directly adopted from the Latin fungus, used in the writings of Horace, a group of all the fungi present in a particular area or geographic region is known as mycobiota, e. g. the mycobiota of Ireland. Like plants, fungi grow in soil and, in the case of mushrooms, form conspicuous fruit bodies. The fungi are now considered a kingdom, distinct from both plants and animals, from which they appear to have diverged around one billion years ago. Fungi have membrane-bound cytoplasmic organelles such as mitochondria, sterol-containing membranes and they have a characteristic range of soluble carbohydrates and storage compounds, including sugar alcohols, disaccharides, and polysaccharides
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Eukaryote
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A eukaryote is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota, the presence of a nucleus gives eukaryotes their name, which comes from the Greek εὖ and κάρυον. Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, in addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular or multicellular, only eukaryotes form multicellular organisms consisting of many kinds of tissue made up of different cell types. Eukaryotes can reproduce asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two identical cells. In meiosis, DNA replication is followed by two rounds of division to produce four daughter cells each with half the number of chromosomes as the original parent cell. These act as sex cells resulting from genetic recombination during meiosis, the domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains, Bacteria and Archaea, are prokaryotes and have none of the above features, eukaryotes represent a tiny minority of all living things. However, due to their larger size, eukaryotes collective worldwide biomass is estimated at about equal to that of prokaryotes. Eukaryotes first developed approximately 1. 6–2.1 billion years ago, in 1905 and 1910, the Russian biologist Konstantin Mereschkowsky argued three things about the origin of nucleated cells. Firstly, plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic host, secondly, the host had earlier in evolution formed by symbiosis between an amoeba-like host and a bacteria-like cell that formed the nucleus. Thirdly, plants inherited photosynthesis from cyanobacteria, the split between the prokaryotes and eukaryotes was introduced in the 1960s. The concept of the eukaryote has been attributed to the French biologist Edouard Chatton, the terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in one paragraph, and the idea was effectively ignored until Chattons statement was rediscovered by Stanier. In 1967, Lynn Margulis provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in cells in her paper. In the 1970s, Carl Woese explored microbial phylogenetics, studying variations in 16S ribosomal RNA and this helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts
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Cytolysis
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Cytolysis, or osmotic lysis, occurs when a cell bursts due to an osmotic imbalance that has caused excess water to move into the cell. It occurs in an environment, where water moves into the cell by osmosis and causes its volume to increase to the point where the volume exceeds the membranes capacity. The presence of a cell wall prevents the membrane from bursting, so cytolysis only occurs in animal, Osmotic lysis is often one result of a stroke, because of improper nutrient perfusion and waste removal alter cell metabolism. Such malfunction results in an inflow of extracellular fluid into the cells, Osmotic lysis would be expected to occur when bacterial cells are treated with a hypotonic solution with added lysozyme, which destroys the bacterias cell walls. Different cells and organisms have adapted different ways of preventing cytolysis from occurring, for example, the paramecium uses a contractile vacuole, which rapidly pumps out excessive water to prevent the build-up of water and the otherwise subsequent lysis. Additionally, these protists have cell membranes which are less permeable to water than other species. If the cell can pump out enough solutes so that an environment can be achieved. Cell disruption Crenation Lysis Osmotic pressure Plasmolysis Water intoxication McClendon, Jesse Francis, original from the University of California, Princeton University Press
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Embryophyte
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The Embryophyta are the most familiar group of green plants that form vegetation on earth. Living embryophytes include hornworts, liverworts, mosses, ferns, lycophytes, gymnosperms and flowering plants, the Embryophyta are informally called land plants because they live primarily in terrestrial habitats, while the related green algae are primarily aquatic. All are complex multicellular eukaryotes with specialized reproductive organs, the name derives from their innovative characteristic of nurturing the young embryo sporophyte during the early stages of its multicellular development within the tissues of the parent gametophyte. With very few exceptions, embryophytes obtain their energy by photosynthesis, the evolutionary origins of the embryophytes are discussed further below, but they are believed to have evolved from within a group of complex green algae during the Paleozoic era. Charales or the stoneworts may be the best living illustration of that developmental step, embryophytes are primarily adapted for life on land, although some are secondarily aquatic. Accordingly, they are called land plants or terrestrial plants. On a microscopic level, the cells of embryophytes are broadly similar to those of green algae and they are eukaryotic, with a cell wall composed of cellulose and plastids surrounded by two membranes. Embryophyte cells also generally have a central vacuole enclosed by a vacuolar membrane or tonoplast. In common with all groups of multicellular algae they have a cycle which involves alternation of generations. The mature sporophyte produces spores which grow into a gametophyte. Embryophytes have two related to their reproductive cycles which distinguish them from all other plant lineages. Firstly, their gametophytes produce sperm and eggs in multicellular structures and this second feature is the origin of the term embryophyte – the fertilized egg develops into a protected embryo, rather than dispersing as a single cell. In the bryophytes the sporophyte dependent on the gametophyte, while in all other embryophytes the sporophyte generation is dominant. Embryophytes also differ from algae by having metamers, metamers are repeated units of development, in which each unit derives from a single cell, but the resulting product tissue or part is largely the same for each cell. The whole organism is thus constructed from similar, repeating parts or metamers, accordingly, these plants are sometimes termed metaphytes and classified as the group Metaphyta. All green algae and land plants are now known to form an evolutionary lineage or clade. According to several molecular clock estimates the Viridiplantae split 1,200 million years ago to 725 million years ago into two clades, chlorophytes and streptophytes, the chlorophytes are considerably more diverse and were originally marine, although some groups have since spread into fresh water. The streptophyte algae are less diverse and adapted to fresh very early in their evolutionary history
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Cellulose
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Cellulose is an organic compound with the formula n, a polysaccharide consisting of a linear chain of several hundred to many thousands of β linked D-glucose units. Cellulose is an important structural component of the cell wall of green plants, many forms of algae. Some species of bacteria secrete it to form biofilms, Cellulose is the most abundant organic polymer on Earth. The cellulose content of cotton fiber is 90%, that of wood is 40–50%, Cellulose is mainly used to produce paperboard and paper. Smaller quantities are converted into a variety of derivative products such as cellophane. Conversion of cellulose from energy crops into biofuels such as ethanol is under investigation as an alternative fuel source. Cellulose for industrial use is mainly obtained from wood pulp and cotton, some animals, particularly ruminants and termites, can digest cellulose with the help of symbiotic micro-organisms that live in their guts, such as Trichonympha. In humans, cellulose acts as a bulking agent for feces and is often referred to as a dietary fiber. Cellulose was discovered in 1838 by the French chemist Anselme Payen, Cellulose was used to produce the first successful thermoplastic polymer, celluloid, by Hyatt Manufacturing Company in 1870. Production of rayon from cellulose began in the 1890s and cellophane was invented in 1912, hermann Staudinger determined the polymer structure of cellulose in 1920. The compound was first chemically synthesized in 1992, by Kobayashi, Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30 degrees, is insoluble in water and most organic solvents, is chiral and is biodegradable. It was shown to melt at 467 °C in 2016 and it can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature. Cellulose is derived from D-glucose units, which condense through β-glycosidic bonds and this linkage motif contrasts with that for α-glycosidic bonds present in starch and glycogen. This confers tensile strength in cell walls, where cellulose microfibrils are meshed into a polysaccharide matrix, compared to starch, cellulose is also much more crystalline. Whereas starch undergoes a crystalline to amorphous transition when heated beyond 60–70 °C in water, cellulose requires a temperature of 320 °C, several different crystalline structures of cellulose are known, corresponding to the location of hydrogen bonds between and within strands. Natural cellulose is cellulose I, with structures Iα and Iβ, Cellulose produced by bacteria and algae is enriched in Iα while cellulose of higher plants consists mainly of Iβ. Cellulose in regenerated cellulose fibers is cellulose II, the conversion of cellulose I to cellulose II is irreversible, suggesting that cellulose I is metastable and cellulose II is stable. With various chemical treatments it is possible to produce the structures cellulose III, many properties of cellulose depend on its chain length or degree of polymerization, the number of glucose units that make up one polymer molecule
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Hemicellulose
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A hemicellulose is any of several heteropolymers, such as arabinoxylans, present along with cellulose in almost all plant cell walls. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random and it is easily hydrolyzed by dilute acid or base as well as myriad hemicellulase enzymes. Hemicelluloses include xylan, glucuronoxylan, arabinoxylan, glucomannan, and xyloglucan and these polysaccharides contain many different sugar monomers. In contrast, cellulose contains only anhydrous glucose, for instance, besides glucose, sugar monomers in hemicellulose can include xylose, mannose, galactose, rhamnose, and arabinose. Hemicelluloses contain most of the D-pentose sugars, and occasionally small amounts of L-sugars as well, xylose is in most cases the sugar monomer present in the largest amount, although in softwoods mannose can be the most abundant sugar. Not only regular sugars can be found in hemicellulose, but also their acidified form, for instance glucuronic acid, Hemicellulose is often associated with cellulose, but it has different composition. Unlike cellulose, hemicellulose consists of shorter chains – 500–3,000 sugar units as opposed to 7, 000–15,000 glucose molecules per polymer, in addition, hemicellulose is a branched polymer, while cellulose is unbranched. Hemicelluloses are embedded in the walls of plants, sometimes in chains that form a ground - they bind with pectin to cellulose to form a network of cross-linked fibres. Hemicelluloses are synthesised from sugar nucleotides in the cells Golgi apparatus, after synthesis, hemicelluloses are transported to the plasma membrane via Golgi vesicles. As percent content of hemicellulose increases in animal feed, the voluntary feed intake decreases, Hemicellulose is represented by the difference between neutral detergent fiber and acid detergent fiber. Microfibrils are cross-linked together by hemicellulose homopolymers, lignins assist and strengthen the attachment of hemicelluloses to microfibrils. Hemicellulose found in trees is predominantly xylan with some glucomannan, while in softwoods it is mainly rich in galactoglucomannan. The average molecular weight is lower than that of cellulose at less than 30,000, cellulose Lignin Pectin Structure and Properties of Hemicellulose /David Wang’s Wood Chemistry Class
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Pectin
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Pectin is a structural heteropolysaccharide contained in the primary cell walls of terrestrial plants. It was first isolated and described in 1825 by Henri Braconnot and it is produced commercially as a white to light brown powder, mainly extracted from citrus fruits, and is used in food as a gelling agent, particularly in jams and jellies. It is also used in dessert fillings, medicines, sweets, as a stabilizer in fruit juices and milk drinks, and as a source of dietary fiber. In plant biology, pectin consists of a set of polysaccharides that are present in most primary cell walls and are particularly abundant in the non-woody parts of terrestrial plants. Pectin is a component of the middle lamella, where it helps to bind cells together. The amount, structure and chemical composition of pectin differs among plants, within a plant over time, Pectin is an important cell wall polysaccharide that allows primary cell wall extension and plant growth. A similar process of cell separation caused by the breakdown of pectin occurs in the zone of the petioles of deciduous plants at leaf fall. Pectin is a part of the human diet, but does not contribute significantly to nutrition. The daily intake of pectin from fruits and vegetables can be estimated to be around 5 g, in human digestion, pectin binds to cholesterol in the gastrointestinal tract and slows glucose absorption by trapping carbohydrates. Pectin is thus a soluble dietary fiber, Pectin has been observed to have DNA repair properties. Pectinaceous surface pellicles, which are rich in pectin, create a layer that holds in dew that helps the cell repair its DNA. Consumption of pectin has been shown to reduce cholesterol levels. The mechanism appears to be an increase of viscosity in the intestinal tract, in the large intestine and colon, microorganisms degrade pectin and liberate short-chain fatty acids that have positive influence on health. A study found a mean of 4.5 ppm methanol in the breath of subjects. The mean endogenous methanol production in humans of 0.45 g/d may be metabolized from pectin found in fruit, methanol is poisonous to the central nervous system and may cause blindness, coma, and death. However, in amounts, methanol is a natural endogenous compound found in normal. Pectins, also known as polysaccharides, are rich in galacturonic acid. Several distinct polysaccharides have been identified and characterised within the pectic group, homogalacturonans are linear chains of α--linked D-galacturonic acid
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Lignin
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Lignin is a class of complex organic polymers that form important structural materials in the support tissues of vascular plants and some algae. Lignins are particularly important in the formation of walls, especially in wood and bark, because they lend rigidity. Chemically, lignins are cross-linked phenolic polymers and he named the substance “lignine”, which is derived from the Latin word lignum, meaning wood. It is one of the most abundant organic polymers on Earth, lignin constitutes 30% of non-fossil organic carbon and 20-35% of the dry mass of wood. The Carboniferous Period is in part defined by the evolution of lignin, the composition of lignin varies from species to species. An example of composition from a sample is 63. 4% carbon,5. 9% hydrogen,0. 7% ash. As a biopolymer, lignin is unusual because of its heterogeneity and its most commonly noted function is the support through strengthening of wood in vascular plants. Global commercial production of lignin is around 1.1 million metric tons per year and is used in a range of low volume, niche applications where the form. Lignin fills the spaces in the wall between cellulose, hemicellulose, and pectin components, especially in vascular and support tissues, xylem tracheids, vessel elements. It is covalently linked to hemicellulose and therefore cross-links different plant polysaccharides, conferring mechanical strength to the cell wall and it is particularly abundant in compression wood but scarce in tension wood, which are types of reaction wood. Lignin plays a part in conducting water in plant stems. The polysaccharide components of plant cell walls are highly hydrophilic and thus permeable to water, the crosslinking of polysaccharides by lignin is an obstacle for water absorption to the cell wall. Thus, lignin makes it possible for the vascular tissue to conduct water efficiently. Lignin is present in all plants, but not in bryophytes. However, it is present in red algae, which seems to suggest that the ancestor of plants. This would suggest that its function was structural, it plays this role in the red alga Calliarthron. Another possibility is that the lignins in red algae and in plants are result of convergent evolution, lignin plays a significant role in the carbon cycle, sequestering atmospheric carbon into the living tissues of woody perennial vegetation. Lignin is one of the most slowly decomposing components of dead vegetation, the resulting soil humus, in general, holds nutrients onto its surface, and hence increases its cation exchange capacity and moisture retention, hence it increases the productivity of soil
32.
Carrageenan
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Carrageenans or carrageenins are a family of linear sulphated polysaccharides that are extracted from red edible seaweeds. They are widely used in the industry, for their gelling, thickening. Their main application is in dairy and meat products, due to their binding to food proteins. There are three varieties of carrageenan, which differ in their degree of sulphation. Kappa-carrageenan has one group per disaccharide, Iota-carrageenan has two, and Lambda-carrageenan has three. Gelatinous extracts of the Chondrus crispus seaweed have been used as food additives since approximately the fifteenth century, carrageenan is a vegetarian and vegan alternative to gelatin in some applications or may be used to replace gelatin in confectionery. Carrageenans are large, highly flexible molecules that curl forming helical structures and this gives them the ability to form a variety of different gels at room temperature. They are widely used in the food and other industries as thickening and stabilizing agents, all carrageenans are high-molecular-weight polysaccharides made up of repeating galactose units and 3,6 anhydrogalactose, both sulfated and nonsulfated. The units are joined by alternating α-1,3 and β-1,4 glycosidic linkages, there are three main commercial classes of carrageenan, Kappa forms strong, rigid gels in the presence of potassium ions, it reacts with dairy proteins. It is sourced mainly from Kappaphycus alvarezii, iota forms soft gels in the presence of calcium ions. It is produced mainly from Eucheuma denticulatum, lambda does not gel, and is used to thicken dairy products. The primary differences that influence the properties of kappa, iota, higher levels of ester sulfate lower the solubility temperature of the carrageenan and produce lower strength gels, or contribute to gel inhibition. Many red algal species produce different types of carrageenans during their developmental history, for instance, the genus Gigartina produces mainly kappa carrageenans during its gametophytic stage, and lambda carrageenans during its sporophytic stage. All are soluble in hot water, but in cold water, when used in food products, carrageenan has the EU additive E-number E407 or E407a when present as processed eucheuma seaweed. Technically carrageenan is considered a dietary fibre, the end-product is a kind of jelly similar to pannacotta, tapioca, or blancmange. 5oz rinsed Irish moss is cooked with 8 quarts of water for 10 minutes, hard water should be mixed with 1/2 oz of borax. Two quarts of water are rapidly added to the hot brew. It is then cooled for 24 hours and becomes gelatinous, as of 2011, global sales of carrageenan were estimated at $640 million
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Agar
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Agar or agar-agar is a jelly-like substance, equivalent to vegan gelatin, obtained from algae. It was discovered in the late 1650s or early 1660s, by Mino Tarōzaemon in Japan, where it is called kanten. Agar is derived from the polysaccharide agarose, which forms the structure in the cell walls of certain species of algae. These algae are known as agarophytes and belong to the Rhodophyta phylum, Agar is actually the resulting mixture of two components, the linear polysaccharide agarose, and a heterogeneous mixture of smaller molecules called agaropectin. Throughout history into modern times, agar has been used as an ingredient in desserts throughout Asia. The gelling agent in agar is an unbranched polysaccharide obtained from the walls of some species of red algae, primarily from the genera Gelidium. For commercial purposes, it is derived primarily from Gelidium amansii, in chemical terms, agar is a polymer made up of subunits of the sugar galactose. Agar was discovered in Japan in 1658 by Mino Tarōzaemon, an innkeeper who was said to have discarded surplus seaweed soup, over the following centuries, agar became a common gelling agent in several Southeast Asian cuisines. Agar was first subjected to analysis in 1859 by the French chemist Anselme Payen. Beginning in the late 19th century, agar began to be used heavily as a medium for growing various microbes. Agar was first described for use in microbiology in 1882 by the German microbiologist Walther Hesse, Agar quickly supplanted gelatin as the base of microbiological media, due to its higher melting temperature, allowing microbes to be grown at higher temperatures without the media liquefying. With its newfound use in microbiology, agar production quickly increased and this production centered on Japan which produced most of the worlds agar until World War II. However, with the outbreak of World War II many nations were forced to establish domestic agar industries in order to continue microbiological research, around the time of World War II, approximately 2,500 tons of agar were produced annually. By the mid-1970s, production worldwide had increased dramatically to approximately 10,000 tons each year, since then, production of agar has fluctuated due to unstable and sometimes over-utilized seaweed populations. The word agar comes from agar-agar, the Malay name for red algae from which the jelly is produced and it is also known as Kanten, Japanese isinglass, Ceylon moss or Jaffna moss. Gracilaria lichenoides is specifically referred to as agal-agal or Ceylon agar, Agar consists of a mixture of two polysaccharides, agarose and agaropectin, with agarose making up about 70% of the mixture. Agarose is a polymer, made up of repeating units of agarobiose. Agar exhibits hysteresis, melting at 85 °C and solidifying from 32–40 °C and this property lends a suitable balance between easy melting and good gel stability at relatively high temperatures
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Peptidoglycan
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Peptidoglycan, also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall. The sugar component consists of alternating residues of β- linked N-acetylglucosamine, attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the chain of another strand forming the 3D mesh-like layer. Peptidoglycan serves a role in the bacterial cell wall, giving structural strength. Peptidoglycan is also involved in binary fission during bacterial cell reproduction, the peptidoglycan layer is substantially thicker in gram-positive bacteria than in gram-negative bacteria, with the attachment of the S-layer. Peptidoglycan forms around 90% of the dry weight of gram-positive bacteria, thus, presence of high levels of peptidoglycan is the primary determinant of the characterisation of bacteria as gram-positive. In gram-positive strains, it is important in attachment roles and serotyping purposes, for both gram-positive and gram-negative bacteria, particles of approximately 2 nm can pass through the peptidoglycan. The peptidoglycan layer in the cell wall is a crystal lattice structure formed from linear chains of two alternating amino sugars, namely N-acetylglucosamine and N-acetylmuramic acid. The alternating sugars are connected by a β--glycosidic bond, peptidoglycan is one of the most important sources of D-amino acids in nature. Cross-linking between amino acids in different linear amino sugar chains occurs with the help of the enzyme DD-transpeptidase and results in a 3-dimensional structure that is strong, the specific amino acid sequence and molecular structure vary with the bacterial species. The peptidoglycan monomers are synthesized in the cytosol and are attached to a membrane carrier bactoprenol. Bactoprenol transports peptidoglycan monomers across the membrane where they are inserted into the existing peptidoglycan. In the first step of peptidoglycan synthesis, the glutamine, which is an acid, donates an amino group to a sugar. This turns fructose 6-phosphate into glucosamine-6-phosphate, in step two, an acetyl group is transferred from acetyl CoA to the amino group on the glucosamine-6-phosphate creating N-acetyl-glucosamine-6-phosphate. In step three of the process, the N-acetyl-glucosamine-6-phosphate is isomerized, which will change N-acetyl-glucosamine-6-phosphate to N-acetyl-glucosamine-1-phosphate. In step 4, the N-acetyl-glucosamine-1-phosphate, which is now a monophosphate, uridine triphosphate, which is a pyrimidine nucleotide, has the ability to act as an energy source. In this particular reaction, after the monophosphate has attacked the UTP and this initial stage, is used to create the precursor for the NAG in peptidoglycan. In step 5, some of the UDP-N-acetylglucosamine is converted to UDP-MurNAc by the addition of a group to the glucosamine
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Archaea
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The Archaea constitute a domain and kingdom of single-celled microorganisms. These microbes are prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles in their cells, Archaea were initially classified as bacteria, receiving the name archaebacteria, but this classification is outdated. Archaeal cells have unique properties separating them from the two domains of life, Bacteria and Eukaryota. The Archaea are further divided into multiple recognized phyla, classification is difficult because the majority have not been isolated in the laboratory and have only been detected by analysis of their nucleic acids in samples from their environment. Archaea and bacteria are generally similar in size and shape, although a few archaea have very strange shapes, such as the flat, other aspects of archaeal biochemistry are unique, such as their reliance on ether lipids in their cell membranes, including archaeols. Archaea use more energy sources than eukaryotes, these range from organic compounds, such as sugars, to ammonia, metal ions or even hydrogen gas. Salt-tolerant archaea use sunlight as a source, and other species of archaea fix carbon, however, unlike plants and cyanobacteria. Archaea reproduce asexually by fission, fragmentation, or budding, unlike bacteria and eukaryotes. They are also found in the colon, oral cavity. Archaea are particularly numerous in the oceans, and the archaea in plankton may be one of the most abundant groups of organisms on the planet, Archaea are a major part of Earths life and may play roles in both the carbon cycle and the nitrogen cycle. No clear examples of archaeal pathogens or parasites are known, one example is the methanogens that inhabit human and ruminant guts, where their vast numbers aid digestion. Methanogens are also used in production and sewage treatment, and enzymes from extremophile archaea that can endure high temperatures. For much of the 20th century, prokaryotes were regarded as a group of organisms and classified based on their biochemistry, morphology. For example, microbiologists tried to classify based on the structures of their cell walls, their shapes. In 1965, Emile Zuckerkandl and Linus Pauling proposed instead using the sequences of the genes in different prokaryotes to work out how they are related to each other and this approach, known as phylogenetics, is the main method used today. Archaea were first classified as a group of prokaryotes in 1977 by Carl Woese. These two groups were named the Archaebacteria and Eubacteria and treated as kingdoms or subkingdoms, which Woese. Woese argued that group of prokaryotes is a fundamentally different sort of life
36.
Glycoprotein
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Glycoproteins are proteins that contain oligosaccharide chains covalently attached to polypeptide side-chains. The carbohydrate is attached to the protein in a cotranslational or posttranslational modification and this process is known as glycosylation. Secreted extracellular proteins are often glycosylated, in proteins that have segments extending extracellularly, the extracellular segments are also often glycosylated. Glycoproteins are also often important integral membrane proteins, where they play a role in cell–cell interactions and it is important to distinguish endoplasmic reticulum-based glycosylation of the secretory system without reversible cytosolic-nuclear glycosylation. In contrast, classical secretory glycosylation can be structurally essential, for example, inhibition of asparagine-linked, i. e. N-linked, glycosylation can prevent glycoprotein folding and full inhibition can be toxic to an individual cell. In contrast, perturbation of terminal processing, which occurs in the Golgi apparatus, is dispensable for isolated cells but can lead to human disease, a famous example of this latter effect is the ABO blood system. There are several types of glycosylation, although the first two are the most common, in N-glycosylation, sugars are attached to nitrogen, typically on the amide side-chain of asparagine. In O-glycosylation, sugars are attached to oxygen, typically on serine or threonine, in P-glycosylation, sugars are attached to phosphorus on a phosphoserine. In C-glycosylation, sugars are attached directly to carbon, such as in the addition of mannose to tryptophan, in glypiation, a GPI glycolipid is attached to the C-terminus of a polypeptide, serving as a membrane anchor. Monosaccharides commonly found in eukaryotic glycoproteins include, The sugar group can assist in protein folding or improve proteins stability, one example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to give them considerable water-holding capacity. Glycoproteins are important for blood cell recognition, especially in mammals. Examples of glycoproteins in the system are, molecules such as antibodies. Molecules of the major histocompatibility complex, which are expressed on the surface of cells, sialyl Lewis X antigen on the surface of leukocytes. H antigen of the ABO blood compatibility antigens, other examples of glycoproteins include, glycoprotein IIb/IIIa, an integrin found on platelets that is required for normal platelet aggregation and adherence to the endothelium. Components of the zona pellucida, which surrounds the oocyte, and is important for sperm-egg interaction, structural glycoproteins, which occur in connective tissue. These help bind together the fibers, cells, and ground substance of connective tissue and they may also help components of the tissue bind to inorganic substances, such as calcium in bone. Glycoprotein-41 and glycoprotein-120 are HIV viral coat proteins, soluble glycoproteins often show a high viscosity, for example, in egg white and blood plasma
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Polysaccharide
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They range in structure from linear to highly branched. Examples include storage polysaccharides such as starch and glycogen, and structural polysaccharides such as cellulose, polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure, these macromolecules can have distinct properties from their building blocks. They may be amorphous or even insoluble in water, natural saccharides are generally of simple carbohydrates called monosaccharides with general formula n where n is three or more. Examples of monosaccharides are glucose, fructose, and glyceraldehyde, polysaccharides, meanwhile, have a general formula of Cxy where x is usually a large number between 200 and 2500. When the repeating units in the backbone are six-carbon monosaccharides, as is often the case, the general formula simplifies to n. Polysaccharides are an important class of biological polymers and their function in living organisms is usually either structure- or storage-related. Starch is used as a polysaccharide in plants, being found in the form of both amylose and the branched amylopectin. In animals, the structurally similar glucose polymer is the more densely branched glycogen, glycogens properties allow it to be metabolized more quickly, which suits the active lives of moving animals. Cellulose and chitin are examples of structural polysaccharides, cellulose is used in the cell walls of plants and other organisms, and is said to be the most abundant organic molecule on Earth. It has many such as a significant role in the paper and textile industries, and is used as a feedstock for the production of rayon, cellulose acetate, celluloid. Chitin has a structure, but has nitrogen-containing side branches. It is found in arthropod exoskeletons and in the walls of some fungi. It also has multiple uses, including surgical threads, polysaccharides also include callose or laminarin, chrysolaminarin, xylan, arabinoxylan, mannan, fucoidan and galactomannan. Nutrition polysaccharides are common sources of energy, many organisms can easily break down starches into glucose, however, most organisms cannot metabolize cellulose or other polysaccharides like chitin and arabinoxylans. These carbohydrate types can be metabolized by bacteria and protists. Ruminants and termites, for example, use microorganisms to process cellulose, even though these complex carbohydrates are not very digestible, they provide important dietary elements for humans. Called dietary fiber, these carbohydrates enhance digestion among other benefits, the main action of dietary fiber is to change the nature of the contents of the gastrointestinal tract, and to change how other nutrients and chemicals are absorbed
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N-Acetylglucosamine
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N-Acetylglucosamine is a monosaccharide and a derivative of glucose. It is an amide between glucosamine and acetic acid and it has a molecular formula of C8H15NO6, a molar mass of 221.21 g/mol, and it is significant in several biological systems. It is part of a biopolymer in the cell wall, built from alternating units of GlcNAc and N-acetylmuramic acid. This layered structure is called peptidoglycan, GlcNAc is the monomeric unit of the polymer chitin, which forms the outer coverings of insects and crustaceans. It is the component of the radulas of mollusks, the beaks of cephalopods. Polymerized with glucuronic acid, it forms hyaluronan, GlcNAc has been reported to be an inhibitor of elastase release from human polymorphonuclear leukocytes, however this is much weaker than the inhibition seen with N-acetylgalactosamine. It has been proposed as a treatment for diseases. Keratan sulfate Chitin N-Acetyllactosamine synthase N-Acetylgalactosamine Wheat germ agglutinin, a plant lectin that binds to this substrate Re Multiple Sclerosis
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Chitin
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Chitin n is a long-chain polymer of an N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. The structure of chitin is comparable to the cellulose, forming crystalline nanofibrils or whiskers. In terms of function, it may be compared to the protein keratin, chitin has proved versatile for several medicinal, industrial and biotechnological purposes. The English word chitin comes from the French word chitine, which first appeared in 1821 and derived from the Greek word χιτών, a similar word, chiton, refers to a marine animal with a protective shell. The structure of chitin was solved by Albert Hofmann in 1929, chitin is a modified polysaccharide that contains nitrogen, it is synthesized from units of N-acetyl-D-glucosamine. Therefore, chitin may be described as cellulose with one group on each monomer replaced with an acetyl amine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength, in its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. Combined with calcium carbonate, as in the shells of crustaceans and molluscs and this composite material is much harder and stiffer than pure chitin, and is tougher and less brittle than pure calcium carbonate. Another difference between pure and composite forms can be seen by comparing the body wall of a caterpillar to the stiff. The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in biomimicry, scarab beetles in the genus Cyphochilus also utilize chitin to form extremely thin scales that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of nanometres, the multiple scattering of light is thought to play a role in the unusual whiteness of the scales. In addition, some wasps, such as Protopolybia chartergoides, orally secrete material containing predominantly chitin to reinforce the outer nest envelopes. Chitosan is produced commercially by deacetylation of chitin, chitosan is soluble in water, chitin producing organisms like protozoa, fungi, arthropods, and nematodes are often pathogens in other species. Keratinocytes in skin can also react to chitin or chitin fragments, according to in vitro studies, chitin is sensed by receptors, such as FIBCD1, KLRB1, REG3G, Toll-like receptor 2, CLEC7A, and mannose receptors. Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1, the first chitin receptor was cloned in 2006. When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, commensal fungi that have ways to interact with the host immune response that as of 2016 were not well understood. Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors, zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins, it is a major pest in wheat crops. Chitin was probably present in the exoskeletons of Cambrian arthropods such as trilobites, the oldest preserved chitin dates to the Oligocene, about 25 million years ago, consisting of a scorpion encased in amber
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Diatom
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Diatoms are a major group of algae, and are among the most common types of phytoplankton. Diatoms are unicellular, although they can form colonies in the shape of filaments or ribbons, fans, zigzags, the first diatom formally described in scientific literature, the colonial Bacillaria paradoxa, was found in 1783 by Danish naturalist Otto Friedrich Müller. Diatoms are producers within the food chain, a unique feature of diatom cells is that they are enclosed within a cell wall made of silica called a frustule. These frustules show a diversity in form, but are usually almost bilaterally symmetrical. The symmetry is not perfect since one of the valves is slightly larger than the other, fossil evidence suggests that they originated during, or before, the early Jurassic period. Only male gametes of centric diatoms are capable of movement by means of flagella, diatom communities are a popular tool for monitoring environmental conditions, past and present, and are commonly used in studies of water quality. More than 200 genera of living diatoms are known, with an estimated 100,000 extant species, diatoms are a widespread group and can be found in the oceans, in fresh water, in soils, and on damp surfaces. They dominate over phytoplankton in nutrient-rich coastal waters and during oceanic spring blooms since they can more rapidly than phytoplankton. Most live pelagically in open water, although some live as surface films at the water-sediment interface and they are especially important in oceans, where they contribute an estimated 45% of the total oceanic primary production of organic material. Spatial distribution of phytoplankton species is restricted both horizontally and vertically. Though most are microscopic, some species of diatoms can reach up to 2 mm in length, diatoms belong to a large group called the heterokonts, including both autotrophs and heterotrophs. Their yellowish-brown chloroplasts are typical of heterokonts, having four membranes, individuals usually lack flagella, but they are present in male gametes of the centric diatoms and have the usual heterokont structure, except they lack the hairs characteristic in other groups. Most diatoms are nonmotile, as their relatively dense cell walls cause them to readily sink, planktonic forms in open water usually rely on turbulent mixing of the upper layers by the wind to keep them suspended in sunlit surface waters. Some species actively regulate their buoyancy with intracellular lipids to counter sinking, a feature of diatoms is the urea cycle, which links them evolutionarily to animals. This was discovered in research carried out by Andrew Allen, Chris Bowler and their study showed that while diatoms and animals use the urea cycle for different ends, they are seen to be evolutionally linked in such a way that animals and plants are not. Diatom cells are contained within a unique cell wall known as a frustule made up of two valves called thecae, that typically overlap one another. The biogenic silica composing the wall is synthesised intracellularly by the polymerisation of silicic acid monomers. This material is extruded to the cell exterior and added to the wall
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Biogenic silica
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Biogenic silica, also referred to as opal, biogenic opal, or amorphous opaline silica, forms one of the most widespread biogenic minerals. For example, microscopic particles of silica called phytoliths can be found in grasses, silica is an amorphous metal oxide formed by complex inorganic polymerization processes. Chemically, bSi is hydrated silica, which is essential to many plants, silicate, or silicic acid, is an important nutrient in the ocean. These organisms extract dissolved silicate from open ocean waters for the buildup of their particulate silica, or opaline. Some of the scales can also be preserved over time as microfossils in deep-sea sediments, providing a window into modern. Diatoms account for 43% of the primary production, and are responsible for the bulk of silica extraction from ocean waters in the modern ocean. In contrast, oceans of Jurassic and older ages, were characterized by radiolarians as major silica-utilizing phyla, nowadays, radiolarians are the second major producers of suspended amorphous silica in ocean waters. Their distribution ranges from the Arctic to the Antarctic, being most abundant in the equatorial zone, in equatorial Pacific waters, for example, about 16,000 specimens per cubic meter can be observed. Silicate cycling gained increasingly in scientific attention the past decade because of following reasons, secondly, biogenic silica accumulation on the sea floor contains lot of information about where in the ocean export production has occurred on time scales ranging from hundreds to millions of years. For this reason, opal deposition records provide information regarding large-scale oceanographic reorganizations in the geological past. At last, the mean residence time for silicate is approximately 10. This relative short time, makes oceanic silicate concentrations and fluxes sensitive to glacial/interglacial perturbations. The remains of diatoms and other silica-utilizing organisms are found, as opal sediments within pelagic deep-sea deposits, pelagic sediments, containing significant quantities of siliceous biogenic remains, are commonly referred to as siliceous ooze. Siliceous ooze are particularly abundant in the ocean at high latitudes in the northern and southern hemispheres. A striking feature of siliceous ooze distribution is a ca.200 km wide belt stretching across the Southern Ocean, some equatorial regions of upwelling, where nutrients are abundant and productivity is high, are also characterized by local siliceous ooze. Siliceous oozes are composed primarily of the remains of diatoms and radiolarians, diatom ooze occurs mainly in high-latitude areas and along some continental margins, whereas radiolarian ooze are more characteristic of equatorial areas. Siliceous ooze are modified and transformed during burial into bedded cherts, diatoms in both fresh and salt water extract silica from the water to use as a component of their cell walls. Likewise, some protozoa, some sponges, and some plants use silicon as a structural material
42.
Robert Hooke
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Robert Hooke FRS was an English natural philosopher, architect and polymath. Allan Chapman has characterised him as Englands Leonardo, Robert Gunthers Early Science in Oxford, a history of science in Oxford during the Protectorate, Restoration and Age of Enlightenment, devotes five of its fourteen volumes to Hooke. Hooke studied at Wadham College, Oxford during the Protectorate where he became one of a tightly knit group of ardent Royalists led by John Wilkins. Here he was employed as an assistant to Thomas Willis and to Robert Boyle and he built some of the earliest Gregorian telescopes and observed the rotations of Mars and Jupiter. In 1665 he inspired the use of microscopes for scientific exploration with his book, based on his microscopic observations of fossils, Hooke was an early proponent of biological evolution. Much of Hookes scientific work was conducted in his capacity as curator of experiments of the Royal Society, much of what is known of Hookes early life comes from an autobiography that he commenced in 1696 but never completed. Richard Waller mentions it in his introduction to The Posthumous Works of Robert Hooke, the work of Waller, along with John Wards Lives of the Gresham Professors and John Aubreys Brief Lives, form the major near-contemporaneous biographical accounts of Hooke. Robert Hooke was born in 1635 in Freshwater on the Isle of Wight to John Hooke, Robert was the last of four children, two boys and two girls, and there was an age difference of seven years between him and the next youngest. Their father John was a Church of England priest, the curate of Freshwaters Church of All Saints, Robert Hooke was expected to succeed in his education and join the Church. John Hooke also was in charge of a school, and so was able to teach Robert. He was a Royalist and almost certainly a member of a group who went to pay their respects to Charles I when he escaped to the Isle of Wight, Robert, too, grew up to be a staunch monarchist. As a youth, Robert Hooke was fascinated by observation, mechanical works and he dismantled a brass clock and built a wooden replica that, by all accounts, worked well enough, and he learned to draw, making his own materials from coal, chalk and ruddle. Hooke quickly mastered Latin and Greek, made study of Hebrew. Here, too, he embarked on his study of mechanics. It appears that Hooke was one of a group of students whom Busby educated in parallel to the work of the school. Contemporary accounts say he was not much seen in the school, in 1653, Hooke secured a choristers place at Christ Church, Oxford. He was employed as an assistant to Dr Thomas Willis. There he met the natural philosopher Robert Boyle, and gained employment as his assistant from about 1655 to 1662, constructing, operating and he did not take his Master of Arts until 1662 or 1663
43.
Karl Rudolphi
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Karl Asmund Rudolphi was a Swedish-born naturalist, who is credited with being the father of helminthology. Rudolphi was born in Stockholm to German parents and he was awarded his doctorate in 1795, from the University of Greifswald, where he was appointed Professor of Anatomy. He worked widely across the fields of botany, zoology, anatomy and he investigated the anatomy of nerves, carried out studies of plant growth and was an early champion of the view that the cell is the basic structural unit of plants. In 1804, Karl Rudolphi, along with J. H. F, link were awarded the prize for solving the problem of the nature of cells by the Königliche Societät der Wissenschaft, Göttingen, for proving that cells had independent rather than common walls. His first great publication was a study of worms, the Enterozoorum Sive Vermium Intestinalium Historia Naturalis. This is the first publication to describe the Nematoda and his second, the Synopsis cui accedunt mantissima duplex et indices locupletissima was the first work to detail the life cycle of important nematode parasites of humans, such as Ascaris lumbricoides. In 1810 he was appointed Professor of Anatomy and Physiology at the University of Berlin and he served two terms as rector of the University, and founded the |Berlin Zootomical Museum. In 1816, he was elected a member of the Royal Swedish Academy of Sciences. In 1821, Rudolphi published his Grundriss der Physiologie, where he argued that the genus should be divided into species. His work therefore predates scientific racism of the Nazi period in German and Scandinavian countries, Rudolphi died in Berlin in 1832, and was succeeded in his position at the University of Berlin by his greatest student, Johannes Müller. Rudolphi is remembered in numerous species such as the sei whale. He is also commemorated by the German Parasitological Society, who award the Rudolphi Medal for scientific excellence
44.
Johann Heinrich Friedrich Link
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Johann Heinrich Friedrich Link was a German naturalist and botanist. Link was born at Hildesheim as a son of the minister August Heinrich Link and he studied medicine and natural sciences at the Hannoverschen Landesuniversität of Göttingen, and graduated as MD in 1789, promoting on his thesis Flora der Felsgesteine rund um Göttingen. One of teachers was the natural scientist Johann Friedrich Blumenbach. He became a tutor in Göttingen. In 1792 he became the first professor of the new department of chemistry, zoology, during his stay at Rostock, he became an early follower of the antiphlogistic theory of Lavoisier, teaching about the existence of oxygen instead of phlogiston. He was also a proponent of the attempts of Richter to involve mathematics in chemistry, in 1806 he set up the first chemical laboratory at Rostock in the Seminargebäude. He was twice elected rector of the university, in 1793 he married Charlotte Juliane Josephi, sister of his colleague at the university Prof. Wilhelm Josephi. During 1797–1799 he visited Portugal with Count Johann Centurius Hoffmannsegg, a botanist, entomologist and ornithologist from Dresden and this trip made him finally choose botany as his main scientific calling. In 1800 he was elected to the prestigious Leopoldina Academy, the oldest school for history in Europe. In 1808 he was awarded a prize at the Academy of Saint Petersburg for his monography Von der Natur und den Eigenschaften des Lichts and his scientific reputation grew and became widely known. In 1811 he was appointed professor of chemistry and botany at Breslau university, after the death of Carl Ludwig Willdenow in 1815, he became professor of natural history, curator of the herbarium and director of the botanic garden in Berlin until he died. This period became the most fruitful period of his academic life and he augmented the collection of the garden to 14,000 specimens, many of them rare plants. He worked in collaboration with Cristoph Friedrich Otto, conservator at the botanical garden. In 1827 he named him the cacti genera Echinocactus and Melocactus. Most of the fungi that he named, are recognised under the original name. He was elected member of the Berlin Academy of Science and many scientific societies, including the Royal Swedish Academy of Sciences. He trained a new generation of natural scientists, such as Christian Gottfried Ehrenberg. Throughout his life, he traveled extensively throughout Europe and he benefited from his knowledge of foreign languages, including Arabic and ancient Sanskrit
45.
Cell wall
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A cell wall is a structural layer surrounding some types of cells, situated outside the cell membrane. It can be tough, flexible, and sometimes rigid and it provides the cell with both structural support and protection, and also acts as a filtering mechanism. Cell walls are present in most prokaryotes, in algae, plants and fungi, a major function is to act as pressure vessels, preventing over-expansion of the cell when water enters. The composition of cell walls varies between species and may depend on type and developmental stage. The primary cell wall of plants is composed of the polysaccharides cellulose, hemicellulose. Often, other such as lignin, suberin or cutin are anchored to or embedded in plant cell walls. Algae possess walls made of glycoproteins and polysaccharides such as carrageenan, in bacteria, the cell wall is composed of peptidoglycan. The cell walls of archaea have various compositions, and may be formed of glycoprotein S-layers, pseudopeptidoglycan, Fungi possess cell walls made of the glucosamine polymer chitin. Unusually, diatoms have a wall composed of biogenic silica. A plant cell wall was first observed and named by Robert Hooke in 1665, in 1804, Karl Rudolphi and J. H. F. Link proved that cells had independent cell walls, before, it had been thought that cells shared walls and that fluid passed between them this way. The mode of formation of the wall was controversial in the 19th century. Hugo von Mohl advocated the idea that the wall grows by apposition. Carl Nägeli believed that the growth of the wall in thickness, each theory was improved in the following decades, the apposition theory by Eduard Strasburger, and the intussusception theory by Julius Wiesner. In 1930, Ernst Münch coined the term apoplast in order to separate the living symplast from the dead plant region, Cell walls serve similar purposes in those organisms that possess them. They may give cells rigidity and strength, offering protection against mechanical stress, in multicellular organisms, they permit the organism to build and hold a definite shape. Cell walls also limit the entry of large molecules that may be toxic to the cell and they further permit the creation of stable osmotic environments by preventing osmotic lysis and helping to retain water. Their composition, properties, and form may change during the cell cycle, in most cells, the cell wall is flexible, meaning that it will bend rather than holding a fixed shape, but has considerable tensile strength
46.
Hugo von Mohl
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Hugo von Mohl was a German botanist from Stuttgart. He was a son of the Württemberg statesman Benjamin Ferdinand von Mohl, while a pupil at the gymnasium he pursued botany and mineralogy in his leisure time, till in 1823 he entered the University of Tübingen. After graduating with distinction in medicine he went to Munich, where he met a circle of botanists. This seems to have determined his career as a botanist, in 1832 he was appointed professor of botany in Tübingen, a post which he never left. Unmarried, his pleasures were in his laboratory and library, and in perfecting optical apparatus and microscopic preparations and he was largely a self-taught botanist from boyhood, and, little influenced in his opinions even by his teachers, preserved always his independence of view on scientific questions. He received many honours during his lifetime, and was elected fellow of the Royal Society in 1868. He recognized under the name of primordial utricle the protoplasmic lining of the vacuolated cell and these and other observations led to the overthrow of Schleidens theory of origin of cells by free-cell-formation. His contributions to knowledge of the cell-wall were no less remarkable and he first explained the true nature of pits, and showed the cellular origin of vessels and of fibrous cells, he was, in fact, the true founder of the cell theory. Mohls early investigations on the structure of palms, of cycads, following on his early demonstration of the origin of stomata, he wrote a classical paper on their opening and closing. In 1843 he started the weekly Botanische Zeitung in conjunction with Schlechtendal, in 1850, he was elected a foreign member of the Royal Swedish Academy of Sciences. In his latter years his productive activity fell off, doubtless through failing health, translated by Henry E. F. Garnsey, revised by Isaac Bayley Balfour. Oxford, Clarendon Press and Biodiversity Heritage Library and this article incorporates text from a publication now in the public domain, Chisholm, Hugh, ed. article name needed
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