Lysozyme known as muramidase or N-acetylmuramide glycanhydrolase, is an antimicrobial enzyme produced by animals that forms part of the innate immune system. Lysozyme is a glycoside hydrolase that catalyzes the hydrolysis of 1,4-beta-linkages between N-acetylmuramic acid and N-acetyl-D-glucosamine residues in peptidoglycan, the major component of gram-positive bacterial cell wall; this hydrolysis in turn compromises the integrity of bacterial cell walls causing lysis of the bacteria. Lysozyme is abundant in secretions including tears, human milk, mucus, it is present in cytoplasmic granules of the macrophages and the polymorphonuclear neutrophils. Large amounts of lysozyme can be found in egg white. C-type lysozymes are related to alpha-lactalbumin in sequence and structure, making them part of the same family. In humans, the lysozyme enzyme is encoded by the LYZ gene. Lysozyme is thermally stable, with a melting point reaching up to 72 ℃ at pH 5.0. However, in human milk it loses activity quickly at that temperature.
Its isoelectric point is 11.35. In a large range of pH lysozyme can survive; the enzyme functions by attacking and breaking glycosidic bonds in peptidoglycans. The enzyme can break glycosidic bonds in chitin, although not as as true chitinases. Lysozymes active site binds the peptidoglycan molecule in the prominent cleft between its two domains, it attacks peptidoglycans, its natural substrate, between N-acetylmuramic acid and the fourth carbon atom of N-acetylglucosamine. Shorter saccharides like tetrasaccharide have shown to be viable substrates but via an intermediate with a longer chain. Chitin has been shown to be a viable lysozyme substrate. Artificial substrates have been developed and used in lysozyme; the Phillips Mechanism proposed that the enzyme's catalytic power came from both steric strain on the bound substrate and electrostatic stabilization of an oxo-carbenium intermediate. From X-ray crystallographic data, Phillips proposed the active site of the enzyme, where a hexasaccharide binds.
The lysozyme distorts the fourth sugar in the hexasaccharide into a half-chair conformation. In this stressed state, the glycosidic bond is more broken. An ionic intermediate containing an oxo-carbenium is created as a result of the glycosidic bond breaking, thus distortion causing the substrate molecule to adopt a strained conformation similar to that of the transition state will lower the energy barrier of the reaction. The proposed oxo-carbonium intermediate was speculated to be electrostatically stabilized by aspartate and glutamate residues in the active site by Arieh Warshel in 1978; the electrostatic stabilization argument was based on comparison to bulk water, the reorientation of water dipoles can cancel out the stabilizing energy of charge interaction. In Warshel's model, the enzyme acts as a super-sovlent, which fixes the orientation of ion pairs and provides super-solvation, lower the energy when to ions are close to each other; the rate-determining step in this mechanism is related to formation of the oxo-carbenium intermediate.
There were some contradictory results to indicate the exact RDS. By tracing the formation of product, it was discovered that the RDS can change over different temperatures, a reason for those contradictory results. At a higher temperature the RDS is formation of glycosyl enzyme intermediate and at a lower temperature the break down of that intermediate. In an early debate in 1969, Dahlquist proposed a covalent mechanism for lysozyme based on kinetic isotope effect, but for a long time the ionic mechanism was more accepted. In 2001, a revised mechanism was proposed by Vocadlo via a covalent but not ionic intermediate. Evidence from ESI-MS analysis indicated a covalent intermediate. A 2-fluoro substituted substrate was used to lower the reaction rate and accumulate an intermediate for characterization; the amino acid side-chains glutamic acid 35 and aspartate 52 have been found to be critical to the activity of this enzyme. Glu35 acts as a proton donor to the glycosidic bond, cleaving the C-O bond in the substrate, whereas Asp52 acts as a nucleophile to generate a glycosyl enzyme intermediate.
The Glu35 reacts with water to form hydroxyl ion, a stronger nucleophile than water, which attacks the glycosyl enzyme intermediate, to give the product of hydrolysis and leaving the enzyme unchanged. This covalent mechanism was named after Koshland. More quantum mechanics/ molecular mechanics molecular dynamics simulations have been using the crystal of HEWL and predict the existence of a covalent intermediate. Evidence for the ESI-MS and X-ray structures indicate the existence of covalent intermediate, but rely on using a less active mutant or non-native substrate. Thus, QM/MM molecular dynamics provides the unique ability to directly investigate the mechanism of wild-type HEWL and native substrate; the calculations revealed that the covalent intermediate from the Koshland mechanism is ~30 kcal/mol more stable than the ionic intermediate from the Phillips mechanism. These calculation demonstrate that the ionic intermediate is energetically unfavorable and the covalent intermediates observed from experiments using less active mutant or non-native substrates provide useful insight into the mechanism of wild-type HEWL.
Imidazole derivatives can form a charge-transfer complex with some residues to achieve a competitive inhibition of lysozyme. In Gram-negative bacteria, the lipopolysaccharide acts as a non-competitive inhib
Gelatin or gelatine is a translucent, flavorless food ingredient, derived from collagen taken from animal body parts. Brittle when dry and gummy when moist, it is called hydrolyzed collagen, collagen hydrolysate, gelatine hydrolysate, hydrolyzed gelatine, collagen peptides, it is used as a gelling agent in food, medications and vitamin capsules, photographic films and papers, cosmetics. Substances containing gelatin or functioning in a similar way are "gelatinous". Gelatin is an irreversibly hydrolyzed form of collagen, wherein the hydrolysis reduces protein fibrils into smaller peptides. Gelatin is in gelatin desserts. Gelatin for cooking comes as powder and sheets. Instant types can be added to the food. Hydrolysis results in the reduction of collagen protein fibrils of about 300,000 Da into smaller peptides. Depending upon the process of hydrolysis, peptides will have broad molecular weight ranges associated with physical and chemical methods of denaturation; the amino acid content of hydrolyzed collagen is the same as collagen.
Hydrolyzed collagen contains 19 amino acids, predominantly glycine and hydroxyproline, which together represent around 50% of the total amino acid content. Hydrolyzed collagen contains 8 out of 9 essential amino acids, including glycine and arginine—two amino-acid precursors necessary for the biosynthesis of creatine, it contains no tryptophan and is deficient in isoleucine and methionine. The bioavailability of hydrolyzed collagen in mice was demonstrated in a 1999 study. A 2005 study in humans found hydrolyzed collagen absorbed as small peptides in the blood. Ingestion of hydrolyzed collagen may affect the skin by increasing the density of collagen fibrils and fibroblasts, thereby stimulating collagen production, it has been suggested, based on mouse and in vitro studies, that hydrolyzed collagen peptides have chemotactic properties on fibroblasts or an influence on growth of fibroblasts. Some clinical studies report that the oral ingestion of hydrolyzed collagen decreases joint pain, those with the most severe symptoms showing the most benefit.
Beneficial action is due to hydrolyzed collagen accumulation in the cartilage and stimulated production of collagen by the chondrocytes, the cells of cartilage. Several studies have shown that a daily intake of hydrolyzed collagen increases bone mass density in rats, it seems that hydrolyzed collagen peptides stimulated differentiation and osteoblasts activity - the cells that build bone - over that of osteoclasts. However, other clinical trials have yielded mixed results. In 2011, the European Food Safety Authority Panel on Dietetic Products and Allergies concluded that "a cause and effect relationship has not been established between the consumption of collagen hydrolysate and maintenance of joints". Four other studies reported benefit with no side effects. One study found that oral collagen only improved symptoms in a minority of patients and reported nausea as a side effect. Another study reported no improvement in disease activity in patients with rheumatoid arthritis. Another study found that collagen treatment may cause an exacerbation of rheumatoid arthritis symptoms.
Hydrolyzed collagen, like gelatin, is made from animal by-products from the meat industry, including skin and connective tissue. In 1997, the U. S. Food and Drug Administration, with support from the TSE Advisory Committee, began monitoring the potential risk of transmitting animal diseases bovine spongiform encephalopathy known as mad cow disease. An FDA study from that year stated: "...steps such as heat, alkaline treatment, filtration could be effective in reducing the level of contaminating TSE agents. On March 18, 2016 the FDA finalized three previously-issued interim final rules designed to further reduce the potential risk of BSE in human food; the final rule clarified that "gelatin is not considered a prohibited cattle material if it is manufactured using the customary industry processes specified."The Scientific Steering Committee of the European Union in 2003 stated that the risk associated with bovine bone gelatin is low or zero. In 2006, the European Food Safety Authority stated that the SSC opinion was confirmed, that the BSE risk of bone-derived gelatin was small, that it recommended removal of the 2003 request to exclude the skull and vertebrae of bovine origin older than 12 months from the material used in gelatin manufacturing.
In cosmetics, hydrolyzed collagen may be found in topical creams, acting as a product texture conditioner, moisturizer. Gelatin is a mixture of peptides and proteins produced by partial hydrolysis of collagen extracted from the skin and connective tissues of animals such as domesticated cattle, chicken and fish. During hydrolysis, the natural molecular bonds between individual collagen strands are broken down into a form that rearranges more easily, its chemical composition is, in many aspects similar to that of its parent collagen. P
Gram-positive bacteria are bacteria that give a positive result in the Gram stain test, traditionally used to classify bacteria into two broad categories according to their cell wall. Gram-positive bacteria take up the crystal violet stain used in the test, appear to be purple-coloured when seen through a microscope; this is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Gram-negative bacteria cannot retain the violet stain after the decolorization step, their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counterstain and appear red or pink. Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to certain cell wall targeting antibiotics than gram-negative bacteria, due to the absence of the outer membrane. In general, the following characteristics are present in gram-positive bacteria: Cytoplasmic lipid membrane Thick peptidoglycan layer Teichoic acids and lipoids are present, forming lipoteichoic acids, which serve as chelating agents, for certain types of adherence.
Peptidoglycan chains are cross-linked to form rigid cell walls by a bacterial enzyme DD-transpeptidase. A much smaller volume of periplasm than that in gram-negative bacteria. Only some species have a capsule consisting of polysaccharides. Only some species are flagellates, when they do have flagella, have only two basal body rings to support them, whereas gram-negative have four. Both gram-positive and gram-negative bacteria have a surface layer called an S-layer. In gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Gram-negative bacteria's S-layer is attached directly to the outer membrane. Specific to gram-positive bacteria is the presence of teichoic acids in the cell wall; some of these are lipoteichoic acids, which have a lipid component in the cell membrane that can assist in anchoring the peptidoglycan. Along with cell shape, Gram staining is a rapid method used to differentiate bacterial species; such staining, together with growth requirement and antibiotic susceptibility testing, other macroscopic and physiologic tests, forms the full basis for classification and subdivision of the bacteria.
The kingdom Monera was divided into four divisions based on Gram staining: Firmicutes, Gracilicutes and Mendocutes. Based on 16S ribosomal RNA phylogenetic studies of the late microbiologist Carl Woese and collaborators and colleagues at the University of Illinois, the monophyly of the gram-positive bacteria was challenged, with major implications for the therapeutic and general study of these organisms. Based on molecular studies of the 16S sequences, Woese recognised twelve bacterial phyla. Two of these were both gram-positive and were divided on the proportion of the guanine and cytosine content in their DNA; the high G + C phylum was made up of the Actinobacteria and the low G + C phylum contained the Firmicutes. The Actinobacteria include the Corynebacterium, Mycobacterium and Streptomyces genera; the Firmicutes, have a 45 -- 60 % GC content. Although bacteria are traditionally divided into two main groups, gram-positive and gram-negative, based on their Gram stain retention property, this classification system is ambiguous as it refers to three distinct aspects, which do not coalesce for some bacterial species.
The gram-positive and gram-negative staining response is not a reliable characteristic as these two kinds of bacteria do not form phylogenetic coherent groups. However, although Gram staining response is an empirical criterion, its basis lies in the marked differences in the ultrastructure and chemical composition of the bacterial cell wall, marked by the absence or presence of an outer lipid membrane. All gram-positive bacteria are bounded by a single-unit lipid membrane, and, in general, they contain a thick layer of peptidoglycan responsible for retaining the Gram stain. A number of other bacteria—that are bounded by a single membrane, but stain gram-negative due to either lack of the peptidoglycan layer, as in the Mycoplasmas, or their inability to retain the Gram stain because of their cell wall composition—also show close relationship to the Gram-positive bacteria. For the bacterial cells bounded by a single cell membrane, the term "monoderm bacteria" or "monoderm prokaryotes" has been proposed.
In contrast to gram-positive bacteria, all archetypical gram-negative bacteria are bounded by a cytoplasmic membrane and an outer cell membrane. The presence of inner and outer cell membranes defines a new compartment in these cells: the periplasmic space or the periplasmic compartment; these bacteria have been designated as "diderm bacteria." The distinction between the monoderm and diderm bacteria is supported by conserved signature indels in a number of important proteins. Of these two structurally distinct groups of bacteria, monoderms are indicated to be ancestral. Based upon a number of observations including that the gram-positive bacteria are the major producers of antibiotics and that, in general, gram-negative bacteria are resistant to them, it h
Bacteria are a type of biological cell. They constitute a large domain of prokaryotic microorganisms. A few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals. Bacteria were among the first life forms to appear on Earth, are present in most of its habitats. Bacteria inhabit soil, acidic hot springs, radioactive waste, the deep portions of Earth's crust. Bacteria live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, only about half of the bacterial phyla have species that can be grown in the laboratory; the study of bacteria is known as a branch of microbiology. There are 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh water. There are 5×1030 bacteria on Earth, forming a biomass which exceeds that of all plants and animals. Bacteria are vital in many stages of the nutrient cycle by recycling nutrients such as the fixation of nitrogen from the atmosphere.
The nutrient cycle includes the decomposition of dead bodies. In the biological communities surrounding hydrothermal vents and cold seeps, extremophile bacteria provide the nutrients needed to sustain life by converting dissolved compounds, such as hydrogen sulphide and methane, to energy. Data reported by researchers in October 2012 and published in March 2013 suggested that bacteria thrive in the Mariana Trench, with a depth of up to 11 kilometres, is the deepest known part of the oceans. Other researchers reported related studies that microbes thrive inside rocks up to 580 metres below the sea floor under 2.6 kilometres of ocean off the coast of the northwestern United States. According to one of the researchers, "You can find microbes everywhere—they're adaptable to conditions, survive wherever they are."The famous notion that bacterial cells in the human body outnumber human cells by a factor of 10:1 has been debunked. There are 39 trillion bacterial cells in the human microbiota as personified by a "reference" 70 kg male 170 cm tall, whereas there are 30 trillion human cells in the body.
This means that although they do have the upper hand in actual numbers, it is only by 30%, not 900%. The largest number exist in the gut flora, a large number on the skin; the vast majority of the bacteria in the body are rendered harmless by the protective effects of the immune system, though many are beneficial in the gut flora. However several species of bacteria are pathogenic and cause infectious diseases, including cholera, anthrax and bubonic plague; the most common fatal bacterial diseases are respiratory infections, with tuberculosis alone killing about 2 million people per year in sub-Saharan Africa. In developed countries, antibiotics are used to treat bacterial infections and are used in farming, making antibiotic resistance a growing problem. In industry, bacteria are important in sewage treatment and the breakdown of oil spills, the production of cheese and yogurt through fermentation, the recovery of gold, palladium and other metals in the mining sector, as well as in biotechnology, the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetes, bacteria are now classified as prokaryotes. Unlike cells of animals and other eukaryotes, bacterial cells do not contain a nucleus and harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in the 1990s that prokaryotes consist of two different groups of organisms that evolved from an ancient common ancestor; these evolutionary domains are called Archaea. The word bacteria is the plural of the New Latin bacterium, the latinisation of the Greek βακτήριον, the diminutive of βακτηρία, meaning "staff, cane", because the first ones to be discovered were rod-shaped; the ancestors of modern bacteria were unicellular microorganisms that were the first forms of life to appear on Earth, about 4 billion years ago. For about 3 billion years, most organisms were microscopic, bacteria and archaea were the dominant forms of life. Although bacterial fossils exist, such as stromatolites, their lack of distinctive morphology prevents them from being used to examine the history of bacterial evolution, or to date the time of origin of a particular bacterial species.
However, gene sequences can be used to reconstruct the bacterial phylogeny, these studies indicate that bacteria diverged first from the archaeal/eukaryotic lineage. The most recent common ancestor of bacteria and archaea was a hyperthermophile that lived about 2.5 billion–3.2 billion years ago. Bacteria were involved in the second great evolutionary divergence, that of the archaea and eukaryotes. Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations with the ancestors of eukaryotic cells, which were themselves related to the Archaea; this involved the engulfment by proto-eukaryotic cells of alphaproteobacterial symbionts to form either mitochondria or hydrogenosomes, which are still found in all known Eukarya. Some eukaryotes that contained mitochondria engulfed cyanobacteria-like organisms, leading to the formation of chloroplasts in algae and plants; this is known as primary endosymbiosis. Bacteria display a wide diversity of sizes, called morphologies.
Bacterial cells are about one-tenth the size of eukaryotic cells
Protein Data Bank
The Protein Data Bank is a database for the three-dimensional structural data of large biological molecules, such as proteins and nucleic acids. The data obtained by X-ray crystallography, NMR spectroscopy, or cryo-electron microscopy, submitted by biologists and biochemists from around the world, are accessible on the Internet via the websites of its member organisations; the PDB is overseen by an organization called the Worldwide Protein Data Bank, wwPDB. The PDB is a key in areas such as structural genomics. Most major scientific journals, some funding agencies, now require scientists to submit their structure data to the PDB. Many other databases use protein structures deposited in the PDB. For example, SCOP and CATH classify protein structures, while PDBsum provides a graphic overview of PDB entries using information from other sources, such as Gene ontology. Two forces converged to initiate the PDB: 1) a small but growing collection of sets of protein structure data determined by X-ray diffraction.
In 1969, with the sponsorship of Walter Hamilton at the Brookhaven National Laboratory, Edgar Meyer began to write software to store atomic coordinate files in a common format to make them available for geometric and graphical evaluation. By 1971, one of Meyer's programs, SEARCH, enabled researchers to remotely access information from the database to study protein structures offline. SEARCH was instrumental in enabling networking, thus marking the functional beginning of the PDB; the Protein Data Bank was announced in October 1971 in Nature New Biology as a joint venture between Cambridge Crystallographic Data Centre, UK and Brookhaven National Laboratory, USA. Upon Hamilton's death in 1973, Tom Koeztle took over direction of the PDB for the subsequent 20 years. In January 1994, Joel Sussman of Israel's Weizmann Institute of Science was appointed head of the PDB. In October 1998, the PDB was transferred to the Research Collaboratory for Structural Bioinformatics; the new director was Helen M. Berman of Rutgers University.
In 2003, with the formation of the wwPDB, the PDB became an international organization. The founding members are PDBe, RCSB, PDBj; the BMRB joined in 2006. Each of the four members of wwPDB can act as deposition, data processing and distribution centers for PDB data; the data processing refers to the fact that annotate each submitted entry. The data are automatically checked for plausibility; the PDB database is updated weekly. The PDB holdings list is updated weekly; as of 17 October 2018, the breakdown of current holdings is as follows: 120,052 structures in the PDB have a structure factor file. 9,734 structures have an NMR restraint file. 3,486 structures in the PDB have a chemical shifts file. 2,531 structures in the PDB have a 3DEM map file deposited in EM Data BankThese data show that most structures are determined by X-ray diffraction, but about 10% of structures are now determined by protein NMR. When using X-ray diffraction, approximations of the coordinates of the atoms of the protein are obtained, whereas estimations of the distances between pairs of atoms of the protein are found through NMR experiments.
Therefore, the final conformation of the protein is obtained, in the latter case, by solving a distance geometry problem. A few proteins are determined by cryo-electron microscopy; the significance of the structure factor files, mentioned above, is that, for PDB structures determined by X-ray diffraction that have a structure file, the electron density map may be viewed. The data of such structures is stored on the "electron density server". In the past, the number of structures in the PDB has grown at an exponential rate, passing the 100 registered structures milestone in 1982, the 1,000 in 1993, the 10,000 in 1999, the 100,000 in 2014. However, since 2007, the rate of accumulation of new protein structures appears to have plateaued; the file format used by the PDB was called the PDB file format. This original format was restricted by the width of computer punch cards to 80 characters per line. Around 1996, the "macromolecular Crystallographic Information file" format, mmCIF, an extension of the CIF format started to be phased in.
MmCIF is now the master format for the PDB archive. An XML version of this format, called PDBML, was described in 2005; the structure files can be downloaded in any of these three formats. In fact, individual files are downloaded into graphics packages using web addresses: For PDB format files, use, e.g. http://www.pdb.org/pdb/files/4hhb.pdb.gz or http://pdbe.org/download/4hhb For PDBML files, use, e.g. http://www.pdb.org/pdb/files/4hhb.xml.gz or http://pdbe.org/pdbml/4hhbThe "4hhb" is the PDB identifier. Each structure published in PDB receives a four-character alphanumeric identifier, its PDB ID; the structure files may be viewed using one of several free and open source computer programs, including Jmol, Pymol, VMD, Rasmol. Other non-free, shareware programs
In biology, tissue is a cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are formed by the functional grouping together of multiple tissues; the English word "tissue" is derived from the French "tissu", meaning something, "woven", from the verb tisser, "to weave". The study of human and animal tissues is known as histology or, in connection with disease, histopathology. For plants, the discipline is called plant anatomy; the classical tools for studying tissues are the paraffin block in which tissue is embedded and sectioned, the histological stain, the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis.
Animal tissues are grouped into four basic types: connective, muscle and epithelial. Collections of tissues joined in structural units to serve a common function compose organs. While all eumetazoan animals can be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type may differ developmentally for different classifications of animals; the epithelium in all birds and animals is derived from the ectoderm and endoderm, with a small contribution from the mesoderm, forming the endothelium, a specialized type of epithelium that composes the vasculature. By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions, to create a selectively permeable barrier; this tissue covers all organismal surfaces that come in contact with the external environment such as the skin, the airways, the digestive tract.
It serves functions of protection and absorption, is separated from other tissues below by a basal lamina. Connective tissues are fibrous tissues, they are made up of cells separated by non-living material, called an extracellular matrix. This matrix can be rigid. For example, blood contains plasma as its matrix and bone's matrix is rigid. Connective tissue holds them in place. Blood, tendon, ligament and areolar tissues are examples of connective tissues. One method of classifying connective tissues is to divide them into three types: fibrous connective tissue, skeletal connective tissue, fluid connective tissue. Muscle cells form the active contractile tissue of the body known as muscle tissue or muscular tissue. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle tissue is separated into three distinct categories: visceral or smooth muscle, found in the inner linings of organs. Cells comprising the central nervous system and peripheral nervous system are classified as nervous tissue.
In the central nervous system, neural tissues form spinal cord. In the peripheral nervous system, neural tissues form the cranial nerves and spinal nerves, inclusive of the motor neurons; the epithelial tissues are formed by cells that cover the organ surfaces, such as the surface of skin, the airways, the reproductive tract, the inner lining of the digestive tract. The cells comprising an epithelial layer are linked via tight junctions. In addition to this protective function, epithelial tissue may be specialized to function in secretion and absorption. Epithelial tissue helps to protect organs from microorganisms and fluid loss. Functions of epithelial tissue: The cells of the body's surface form the outer layer of skin. Inside the body, epithelial cells form the lining of the mouth and alimentary canal and protect these organs. Epithelial tissues help in absorption of water and nutrients. Epithelial tissues help in the elimination of waste. Epithelial tissues hormones in the form of glands; some epithelial tissue perform secretory functions.
They secrete a variety of substances such as sweat, enzymes, etc. There are many kinds of epithelium, nomenclature is somewhat variable. Most classification schemes combine a description of the cell-shape in the upper layer of the epithelium with a word denoting the number of layers: either simple or stratified. However, other cellular features, such as cilia may be described in the classification system; some common kinds of epithelium are listed below: Simple squamous epithelium Stratified squamous epithelium Simple cuboidal epithelium Transitional epithelium Pseudostratified columnar epithelium Columnar epithelium Glandular epithelium Ciliated columnar epithelium In plant anatomy, tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, the vascular tissue. Epidermis - Cells forming the outer surface of the leaves and of the young plant body. Vascular tissue - The primary components of vascular tissue are the xylem and phloem; these transport nutrients internally.
Ground tissue - Ground tissue is less differentiated than other tissues. Ground tis
Osmotic pressure is the minimum pressure which needs to be applied to a solution to prevent the inward flow of its pure solvent across a semipermeable membrane. It is defined as the measure of the tendency of a solution to take in pure solvent by osmosis. Potential osmotic pressure is the maximum osmotic pressure that could develop in a solution if it were separated from its pure solvent by a semipermeable membrane. Osmosis occurs when two solutions, containing different concentration of solute, are separated by a selectively permeable membrane. Solvent molecules pass preferentially through the membrane from the low-concentration solution to the solution with higher solute concentration; the transfer of solvent molecules will continue. Jacobus van't Hoff found a quantitative relationship between osmotic pressure and solute concentration, expressed in the following equation. Π = i C R T where Π is osmotic pressure, i is the dimensionless van't Hoff index, C is the molar concentration of solute, R is the ideal gas constant, T is the temperature in kelvins.
This formula applies when the solute concentration is sufficiently low that the solution can be treated as an ideal solution. The proportionality to concentration means. Note the similarity of this formula to the ideal gas law in the form p = n V R T = c gas R T where n is the total number of moles of gas molecules in the volume V, n/V is the molar concentration of gas molecules. Harmon Northrop Morse and Frazer showed that the equation applied to more concentrated solutions if the unit of concentration was molal rather than molar. For more concentrated solutions the van't Hoff equation can be extended as a power series in solute concentration, C. To a first approximation, Π = Π 0 + A C 2 where Π 0 is the ideal pressure and A is an empirical parameter; the value of the parameter A can be used to calculate Pitzer parameters. Empirical parameters are used to quantify the behaviour of solutions of ionic and non-ionic solutes which are not ideal solutions in the thermodynamic sense; the Pfeffer cell was developed for the measurement of osmotic pressure.
Osmotic pressure measurement may be used for the determination of molecular weights. Osmotic pressure is an important factor affecting cells. Osmoregulation is the homeostasis mechanism of an organism to reach balance in osmotic pressure. Hypertonicity is the presence of a solution. Hypotonicity is the presence of a solution. Isotonicity is the presence of a solution; when a biological cell is in a hypotonic environment, the cell interior accumulates water, water flows across the cell membrane into the cell, causing it to expand. In plant cells, the cell wall restricts the expansion, resulting in pressure on the cell wall from within called turgor pressure. Turgor pressure allows herbaceous plants to stand upright, it is the determining factor for how plants regulate the aperture of their stomata. In animal cells excessive osmotic pressure can result in cytolysis. Osmotic pressure is the basis of filtering, a process used in water purification; the water to be purified is placed in a chamber and put under an amount of pressure greater than the osmotic pressure exerted by the water and the solutes dissolved in it.
Part of the chamber opens to a differentially permeable membrane that lets water molecules through, but not the solute particles. The osmotic pressure of ocean water is about 27 atm. Reverse osmosis desalinates fresh water from ocean salt water. Consider the system at the point when it has reached equilibrium; the condition for this is that the chemical potential of the solvent on both sides of the membrane is equal. The compartment containing the pure solvent has a chemical potential of μ 0, where p is the pressure. On the other side, in the compartment containing the solute, the chemical potential of the solvent depends on the mole fraction of the solvent, 0 < x v < 1. Besides, this compartment can assume a different pressure, p ′. We can therefore write the chemical potential of the solvent as μ v. If we write p ′ = p + Π, the balance of the chemical potential is therefore: μ v 0 = μ v. Here, the difference in pressure of the two compartments Π ≡ p ′ − p is defined as the osmotic pressure exerted by the solutes.
Holding the pressure, the addition of solute decreases the chemical potential