1.
Mitosis
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In cell biology, mitosis is a part of the cell cycle when replicated chromosomes are separated into two new nuclei. Mitosis and cytokinesis together define the phase of an animal cell cycle—the division of the mother cell into two daughter cells genetically identical to each other. The process of mitosis is divided into stages corresponding to the completion of one set of activities and these stages are prophase, prometaphase, metaphase, anaphase, and telophase. During mitosis, the chromosomes, which have already duplicated, condense, the result is two genetically identical daughter nuclei. The rest of the cell may then continue to divide by cytokinesis to produce two daughter cells, producing three or more daughter cells instead of normal two is a mitotic error called tripolar mitosis or multipolar mitosis. Other errors during mitosis can induce apoptosis or cause mutations, certain types of cancer can arise from such mutations. Mitosis occurs only in eukaryotic cells, prokaryotic cells, which lack a nucleus, divide by a different process called binary fission. Most animal cells undergo a change, known as mitotic cell rounding. Most human cells are produced by cell division. Important exceptions include the gametes – sperm and egg cells – which are produced by meiosis, german zoologist Otto Bütschli might have claimed the discovery of the process presently known as mitosis, a term coined by Walther Flemming in 1882. Mitosis was discovered in frog, rabbit, and cat cornea cells in 1873, the term is derived from the Greek word μίτος mitos warp thread. The primary result of mitosis and cytokinesis is the transfer of a parent cells genome into two daughter cells, the genome is composed of a number of chromosomes—complexes of tightly coiled DNA that contain genetic information vital for proper cell function. Because each resultant daughter cell should be identical to the parent cell. This occurs during the S phase of interphase, chromosome duplication results in two identical sister chromatids bound together by cohesin proteins at the centromere. When mitosis begins, the chromosomes condense and become visible, in some eukaryotes, for example animals, the nuclear envelope, which segregates the DNA from the cytoplasm, disintegrates into small vesicles. The nucleolus, which makes ribosomes in the cell, also disappears, microtubules project from opposite ends of the cell, attach to the centromeres, and align the chromosomes centrally within the cell. The microtubules then contract to pull the chromatids of each chromosome apart. Sister chromatids at this point are called daughter chromosomes, as the cell elongates, corresponding daughter chromosomes are pulled toward opposite ends of the cell and condense maximally in late anaphase
2.
Chromosome
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A chromosome is a DNA molecule with part or all of the genetic material of an organism. Prokaryotes usually have one single circular chromosome, whereas most eukaryotes are diploid, chromosomes in eukaryotes are composed of chromatin fiber. Chromatin fiber is made of nucleosomes, a nucleosome is a histone octamer with part of a longer DNA strand attached to and wrapped around it. Chromatin fiber, together with associated proteins is known as chromatin, chromatin is present in most cells, with a few exceptions, for example, red blood cells. Occurring only in the nucleus of cells, chromatin contains the vast majority of DNA, except for a small amount inherited maternally. Chromosomes are normally visible under a microscope only when the cell is undergoing the metaphase of cell division. Before this happens every chromosome is copied once, and the copy is joined to the original by a centromere resulting in an X-shaped structure, the original chromosome and the copy are now called sister chromatids. During metaphase, when a chromosome is in its most condensed state, in this highly condensed form chromosomes are easiest to distinguish and study. In prokaryotic cells, chromatin occurs free-floating in cytoplasm, as these cells lack organelles, the main information-carrying macromolecule is a single piece of coiled double-helix DNA, containing many genes, regulatory elements and other noncoding DNA. The DNA-bound macromolecules are proteins that serve to package the DNA, chromosomes vary widely between different organisms. Some species such as certain bacteria also contain plasmids or other extrachromosomal DNA and these are circular structures in the cytoplasm that contain cellular DNA and play a role in horizontal gene transfer. Chromosomal recombination during meiosis and subsequent sexual reproduction plays a significant role in genetic diversity. In prokaryotes and viruses, the DNA is often densely packed and organized, in the case of archaea, by homologs to eukaryotic histones, small circular genomes called plasmids are often found in bacteria and also in mitochondria and chloroplasts, reflecting their bacterial origins. Some use the term chromosome in a sense, to refer to the individualized portions of chromatin in cells. However, others use the concept in a sense, to refer to the individualized portions of chromatin during cell division. The word chromosome comes from the Greek χρῶμα and σῶμα, describing their strong staining by particular dyes, schleiden, Virchow and Bütschli were among the first scientists who recognized the structures now so familiar to everyone as chromosomes. The term was coined by von Waldeyer-Hartz, referring to the term chromatin, in a series of experiments beginning in the mid-1880s, Theodor Boveri gave the definitive demonstration that chromosomes are the vectors of heredity. His two principles were the continuity of chromosomes and the individuality of chromosomes and it is the second of these principles that was so original
3.
Staining
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Staining is an auxiliary technique used in microscopy to enhance contrast in the microscopic image. Stains and dyes are used in biology and medicine to highlight structures in biological tissues for viewing. Stains may be used to define and examine bulk tissues, cell populations, in biochemistry it involves adding a class-specific dye to a substrate to qualify or quantify the presence of a specific compound. Staining and fluorescent tagging can serve similar purposes, biological staining is also used to mark cells in flow cytometry, and to flag proteins or nucleic acids in gel electrophoresis. Simple staining is staining with only one stain/dye, there are various kinds of multiple staining, many of which are examples of counterstaining, differential staining, or both, including double staining and triple staining. In vivo staining is the process of dyeing living tissues—in vivo means in life, by causing certain cells or structures to take on contrasting colour, their form or position within a cell or tissue can be readily seen and studied. In vitro staining involves colouring cells or structures that have removed from their biological context. Certain stains are often combined to reveal more details and features than a single stain alone, combined with specific protocols for fixation and sample preparation, scientists and physicians can use these standard techniques as consistent, repeatable diagnostic tools. A counterstain is stain that makes cells or structures more visible, for example, crystal violet stains only Gram-positive bacteria in Gram staining. A safranin counterstain is applied that stains all cells, allowing identification of Gram-negative bacteria, while ex vivo, many cells continue to live and metabolize until they are fixed. Some staining methods are based on this property and those stains excluded by the living cells but taken up by the already dead cells are called vital stains. Those that enter and stain living cells are called supravital stains, however, these stains are eventually toxic to the organism, some more so than others. To achieve desired effects, the stains are used in very dilute solutions ranging from 1,5000 to 1,500000, note that many stains may be used in both living and fixed cells. The preparatory steps involved depend on the type of analysis planned, fixation–which may itself consist of several steps–aims to preserve the shape of the cells or tissue involved as much as possible. Sometimes heat fixation is used to kill, adhere, and alter the specimen so it accepts stains, most chemical fixatives generate chemical bonds between proteins and other substances within the sample, increasing their rigidity. Common fixatives include formaldehyde, ethanol, methanol, and/or picric acid, pieces of tissue may be embedded in paraffin wax to increase their mechanical strength and stability and to make them easier to cut into thin slices. Permeabilization involves treatment of cells with a mild surfactant and this treatment dissolves cell membranes, and allows larger dye molecules into the cells interior. Mounting usually involves attaching the samples to a microscope slide for observation
4.
Fluorescence in situ hybridization
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Fluorescence in situ hybridization is a cytogenetic technique that uses fluorescent probes that bind to only those parts of the chromosome with a high degree of sequence complementarity. It was developed by researchers in the early 1980s and is used to detect. Fluorescence microscopy can be used to find out where the fluorescent probe is bound to the chromosomes, FISH is often used for finding specific features in DNA for use in genetic counseling, medicine, and species identification. FISH can also be used to detect and localize specific RNA targets in cells, circulating tumor cells, in this context, it can help define the spatial-temporal patterns of gene expression within cells and tissues. RNA probes can be designed for any gene or any sequence within a gene for visualization of mRNA, lncRNA and miRNA in tissues, FISH is used by examining the cellular reproduction cycle, specifically interphase of the nuclei for any chromosomal abnormalities. The hybridization signals for each probe when a nucleic abnormality is detected, each probe for the detection of mRNA and lncRNA is composed of 20 oligonucleotide pairs, each pair covering a space of 40–50 bp. For miRNA detection, the probes use proprietary chemistry for specific detection of miRNA, probes are often derived from fragments of DNA that were isolated, purified, and amplified for use in the Human Genome Project. The size of the genome is so large, compared to the length that could be sequenced directly. To preserve the fragments with their individual DNA sequences, the fragments were added into a system of continually replicating bacteria populations, clonal populations of bacteria, each population maintaining a single artificial chromosome, are stored in various laboratories around the world. The artificial chromosomes can be grown, extracted, and labeled and these fragments are on the order of 100 thousand base-pairs, and are the basis for most FISH probes. Cells, circulating tumor cells, or formalin-fixed paraffin-embedded or frozen tissue sections are fixed, FISH has also been successfully done on unfixed cells. A target-specific probe, composed of 20 oligonucleotide pairs, hybridizes to the target RNA, separate but compatible signal amplification systems enable the multiplex assay. Signal amplification is achieved via series of sequential hybridization steps, at the end of the assay the tissue samples are visualized under a fluorescence microscope. The probe must be enough to hybridize specifically with its target. The probe is tagged directly with fluorophores, with targets for antibodies or with biotin, tagging can be done in various ways, such as nick translation, or PCR using tagged nucleotides. Then, an interphase or metaphase chromosome preparation is produced, the chromosomes are firmly attached to a substrate, usually glass. Repetitive DNA sequences must be blocked by adding short fragments of DNA to the sample, the probe is then applied to the chromosome DNA and incubated for approximately 12 hours while hybridizing. Several wash steps remove all unhybridized or partially hybridized probes, the results are then visualized and quantified using a microscope that is capable of exciting the dye and recording images
5.
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
6.
Microtubule
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Microtubules are a component of the cytoskeleton, found throughout the cytoplasm. These tubular polymers of tubulin can grow as long as 50 micrometres and are highly dynamic, the outer diameter of a microtubule is about 24 nm while the inner diameter is about 12 nm. They are found in cells, as well as some bacteria. Microtubules are very important in a number of cellular processes and they are involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments, they form the cytoskeleton. They also make up the structure of cilia and flagella. They are also involved in chromosome separation, and are the constituents of mitotic spindles. There are many proteins bind to microtubules, including the motor proteins kinesin and dynein, severing proteins like katanin. Recently an actin-like protein has found in a gram-positive bacterium Bacillus thuringiensis. Tubulin and microtubule-mediated processes, like cell locomotion, were seen by early microscopists, in eukaryotes, microtubules are long, hollow cylinders made up of polymerised α- and β-tubulin dimers. The inner space of the hollow microtubule cylinders is referred to as the lumen, the α and β-tubulin subunits are approximately 50% identical at the amino acid level, and each have a molecular weight of approximately 50 kDa. These α/β-tubulin dimers polymerize end-to-end into linear protofilaments that associate laterally to form a single microtubule, typically, microtubules are formed by the parallel association of thirteen protofilaments, although microtubules composed of fewer or more protofilaments have been observed in vitro. Microtubules have a polarity that is critical for their biological function. Tubulin polymerizes end to end, with the β-subunits of one tubulin dimer contacting the α-subunits of the next dimer, therefore, in a protofilament, one end will have the α-subunits exposed while the other end will have the β-subunits exposed. These ends are designated the and ends, respectively, while microtubule elongation can occur at both the and ends, it is significantly more rapid at the end. The lateral association of the protofilaments generates a pseudo-helical structure, with one turn of the helix containing 13 tubulin dimers, each from a different protofilament. In the most common 13-3 architecture, the 13th tubulin dimer interacts with the tubulin dimer with a vertical offset of 3 tubulin monomers due to the helicity of the turn. There are other alternative architectures, such as 11-3, 12-3, 14-3, 15-4, or 16-4, Microtubules can also morph into other forms such as helical filaments, which are observed in protist organisms like foraminifera. There are two types of interactions that can occur between the subunits of lateral protofilaments within the microtubule called the A-type and B-type lattices
7.
Karyotype
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A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. The term is used for the complete set of chromosomes in a species or in an individual organism. Karyotypes describe the chromosome count of an organism and what these chromosomes look like under a light microscope, attention is paid to their length, the position of the centromeres, banding pattern, any differences between the sex chromosomes, and any other physical characteristics. The preparation and study of karyotypes is part of cytogenetics, the study of whole sets of chromosomes is sometimes known as karyology. The chromosomes are depicted in a format known as a karyogram or idiogram, in pairs, ordered by size. The basic number of chromosomes in the cells of an individual or a species is called the somatic number and is designated 2n. In the germ-line the chromosome number is n. p28 Thus, so, in normal diploid organisms, autosomal chromosomes are present in two copies. There may, or may not, be sex chromosomes, polyploid cells have multiple copies of chromosomes and haploid cells have single copies. The study of karyotypes is important for cell biology and genetics, Karyotypes can be used for many purposes, such as to study chromosomal aberrations, cellular function, taxonomic relationships, and to gather information about past evolutionary events. Chromosomes were first observed in plant cells by Carl Wilhelm von Nägeli in 1842 and their behavior in animal cells was described by Walther Flemming, the discoverer of mitosis, in 1882. The name was coined by another German anatomist, Heinrich von Waldeyer in 1888 and it is New Latin from Ancient Greek κάρυον karyon, kernel, seed, or nucleus, and τύπος typos, general form). The next stage took place after the development of genetics in the early 20th century, lev Delaunay seems to have been the first person to define the karyotype as the phenotypic appearance of the somatic chromosomes, in contrast to their genic contents. The subsequent history of the concept can be followed in the works of C. D. Darlington, investigation into the human karyotype took many years to settle the most basic question, how many chromosomes does a normal diploid human cell contain. In 1912, Hans von Winiwarter reported 47 chromosomes in spermatogonia and 48 in oogonia, concluding an XX/XO sex determination mechanism. Painter in 1922 was not certain whether the diploid of humans was 46 or 48, at first favouring 46, but revised his opinion from 46 to 48, considering the techniques of the time, these results were remarkable. In textbooks, the number of human chromosomes remained at 48 for over thirty years, New techniques were needed to correct this error. The work took place in 1955, and was published in 1956, the karyotype of humans includes only 46 chromosomes. Rather interestingly, the apes have 48 chromosomes
8.
Protein
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Proteins are large biomolecules, or macromolecules, consisting of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, responding to stimuli, a linear chain of amino acid residues is called a polypeptide. A protein contains at least one long polypeptide, short polypeptides, containing less than 20–30 residues, are rarely considered to be proteins and are commonly called peptides, or sometimes oligopeptides. The individual amino acid residues are bonded together by peptide bonds, the sequence of amino acid residues in a protein is defined by the sequence of a gene, which is encoded in the genetic code. In general, the code specifies 20 standard amino acids, however. Sometimes proteins have non-peptide groups attached, which can be called prosthetic groups or cofactors, proteins can also work together to achieve a particular function, and they often associate to form stable protein complexes. Once formed, proteins only exist for a period of time and are then degraded and recycled by the cells machinery through the process of protein turnover. A proteins lifespan is measured in terms of its half-life and covers a wide range and they can exist for minutes or years with an average lifespan of 1–2 days in mammalian cells. Abnormal and or misfolded proteins are degraded more rapidly due to being targeted for destruction or due to being unstable. Like other biological macromolecules such as polysaccharides and nucleic acids, proteins are essential parts of organisms, many proteins are enzymes that catalyse biochemical reactions and are vital to metabolism. Proteins also have structural or mechanical functions, such as actin and myosin in muscle and the proteins in the cytoskeleton, other proteins are important in cell signaling, immune responses, cell adhesion, and the cell cycle. In animals, proteins are needed in the diet to provide the essential amino acids that cannot be synthesized, digestion breaks the proteins down for use in the metabolism. Methods commonly used to study structure and function include immunohistochemistry, site-directed mutagenesis, X-ray crystallography, nuclear magnetic resonance. Most proteins consist of linear polymers built from series of up to 20 different L-α-amino acids, all proteinogenic amino acids possess common structural features, including an α-carbon to which an amino group, a carboxyl group, and a variable side chain are bonded. Only proline differs from this structure as it contains an unusual ring to the N-end amine group. The amino acids in a chain are linked by peptide bonds. Once linked in the chain, an individual amino acid is called a residue, and the linked series of carbon, nitrogen. The peptide bond has two forms that contribute some double-bond character and inhibit rotation around its axis, so that the alpha carbons are roughly coplanar
9.
Centrosome
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In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center of the animal cell as well as a regulator of cell-cycle progression. The centrosome is thought to have evolved only in the lineage of eukaryotic cells. Fungi and plants lack centrosomes and therefore use other MTOC structures to organize their microtubules, although the centrosome has a key role in efficient mitosis in animal cells, it is not essential in certain fly and flatworm species. Centrosomes are composed of two orthogonally arranged centrioles surrounded by a mass of protein termed the pericentriolar material. The PCM contains proteins responsible for microtubule nucleation and anchoring including γ-tubulin, pericentrin and ninein, in general, each centriole of the centrosome is based on a nine triplet microtubule assembled in a cartwheel structure, and contains centrin, cenexin and tektin. In many cell type the Centrosome is replaced by a Cilium during cellular difrentiation, however, once the cell start to divide, the cilium is replaced back by the Centrosome. It was discovered by Edouard Van Beneden in 1883, and later described and named in 1888 by Theodor Boveri, centrosomes are associated with the nuclear membrane during prophase of the cell cycle. In mitosis the nuclear membrane breaks down and the centrosome nucleated microtubules can interact with the chromosomes to build the mitotic spindle, the mother centriole, the older of the two in the centriole pair, also has a central role in making cilia and flagella. The centrosome is copied once per cell cycle so that each daughter cell inherits one centrosome. The centrosome replicates during the S phase of the cell cycle, during the prophase in the process of cell division called mitosis, the centrosomes migrate to opposite poles of the cell. The mitotic spindle forms between the two centrosomes. Upon division, each daughter cell receives one centrosome, aberrant numbers of centrosomes in a cell have been associated with cancer. Doubling of a centrosome is similar to DNA replication in two respects, the nature of the process and the action of cdk2 as a regulator of the process. But the processes are different in that centrosome doubling does not occur by template reading. The mother centriole just aids in the accumulation of materials required for the assembly of the daughter centriole, interestingly, centrioles are not required for the progression of mitosis. When the centrioles are irradiated by a laser, mitosis proceeds normally with a morphologically normal spindle, moreover, development of the fruit fly Drosophila is largely normal when centrioles are absent due to a mutation in a gene required for their duplication. In the absence of the centrioles the microtubules of the spindle are focused by motors allowing the formation of a bipolar spindle, many cells can completely undergo interphase without centrioles. Unlike centrioles, centrosomes are required for survival of the organism, acentrosomal cells lack radial arrays of astral microtubules
10.
Cyclin
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Cyclins are a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase enzymes. Cyclins were originally discovered by R. Timothy Hunt in 1982 while studying the cell cycle of sea urchins, in an interview for The Life Scientific hosted by Jim Al-Khalili, R. Timothy Hunt explained that the name cyclin was originally named after his hobby cycling. It was only after the naming did its importance in the cell cycle become apparent, as it was appropriate the name stuck. R. Timothy Hunt, By the way, the cyclin, which I coined, was really a joke, its because I liked cycling so much at the time. Cyclins were originally named because their concentration varies in a fashion during the cell cycle. A cyclin forms a complex with Cdk, which begins to activate the Cdk, complex formation results in activation of the Cdk active site. Cyclins themselves have no enzymatic activity but have binding sites for some substrates, Cyclins, when bound with the dependent kinases, such as the p34/cdc2/cdk1 protein, form the maturation-promoting factor. MPFs activate other proteins through phosphorylation and these phosphorylated proteins, in turn, are responsible for specific events during cycle division such as microtubule formation and chromatin remodeling. Cyclins can be divided into four classes based on their behavior in the cycle of vertebrate somatic cells and yeast cells, G1 cyclins, G1/S cyclins, S cyclins. This division is useful when talking about most cell cycles, G1/S Cyclins rise in late G1 and fall in early S phase. The Cdk- G1/S cyclin complex begins to induce the initial processes of DNA replication, the cyclins also promote other activities to progress the cell cycle, such as centrosome duplication in vertebrates or spindle pole body in yeast. The rise in presence of G1/S cyclins is paralleled by a rise in S cyclins, G1 cyclins do not behave like the other cyclins, in that the concentrations increase gradually, throughout the cell cycle based on cell growth and the external growth-regulatory signals. The presence of G cyclins coordinate cell growth with the entry to a new cell cycle, S cyclins bind to Cdk and the complex directly induces DNA replication. The levels of S cyclins remain high, not only throughout S phase, M cyclin concentrations rise as the cell begins to enter mitosis and the concentrations peak at metaphase. Cell changes in the cell cycle like the assembly of mitotic spindles, the destruction of M cyclins during metaphase and anaphase, after the Spindle Assembly Checkpoint is satisfied, causes the exit of mitosis and cytokinesis. Cyclins are generally different from each other in primary structure. However, all members of the family are similar in 100 amino acids that make up the cyclin box. Cyclins contain two domains of a similar fold, the first located at the N-terminus and the second at the C-terminus
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