In cell biology, mitosis ( ) is part of the cell cycle when the replicated chromosome is separated into two new nuclei. In general, mitosis (nuclear division) is preceded by the phase S interphase (during replicated DNA) and is often accompanied or followed by cytokinesis, which divides the cytoplasm, organelle, and cell membrane into two new cells containing about equal parts of this cellular component. Mitosis and cytokinesis together define the mitosis ( M ) phase of the animal cell cycle - the stem cell division into two child cells is genetically identical other.
The process of mitosis is divided into several stages related to the completion of a set of activities and the beginning of the next. These stages are prophase, prometafase, metaphase, anaphase, and telophase. During mitosis, the chromosomes, which have been duplicated, condense and attach to the spindle fibers that attract one copy of each chromosome to the opposite side of the cell. The result is two genetically identical daughter nuclei. The remaining cells can then continue to divide by the cytokinesis to produce two daughter cells. Producing three or more child cells rather than two normal ones is a mitotic error called mitral triposis or mitotic multipolar (direct cell triplication/multiplication). Other errors during mitosis can induce apoptosis (programmed cell death) or cause mutations. Certain cancers can arise from the mutation.
Mitosis occurs only in eukaryotic cells. Prokaryotic cells, which have no nuclei, are divided by a different process called binary division. Mitosis varies among organisms. For example, animal cells undergo an "open" mitosis, in which the nuclear envelope bursts before the chromosomes are separated, while the fungus undergoes a "closed" mitosis, in which the chromosomes divide in the intact nucleus. Most animal cells undergo form changes, known as mitotic cell divisions, to adopt near spherical morphology at the onset of mitosis. Most human cells are produced by mitotic cell division. Important exceptions include gametes - sperm and egg - produced by meiosis.
Video Mitosis
Discovery
Many descriptions of cell division were made during the 18th and 19th centuries, with varying degrees of accuracy. In 1835, German botanist Hugo von Mohl described cell division in green algae Cladophora glomerata, stating that cell multiplication occurs through cell division. In 1838, Schleiden asserted that the formation of new cells in their interiors is a common law for cell propagation in plants, the views subsequently rejected for the Mohl model, due to the contributions of Robert Remak and others.
In animal cells, cell division with mitosis was found in frogs, rabbits, and cat corneal cells in 1873 and described for the first time by the Polish histologist Wac? Aw Mayzel in 1875.
BÃÆ'¼tschli, Schneider and Fol may also claim the discovery of a process now known as "mitosis". In 1873, the German zoologist Otto BÃÆ'¼tschli published data from observations on nematodes. Several years later, he discovered and described mitosis based on these observations.
The term "mitosis", coined by Walther Flemming in 1882, comes from the Greek word ????? ( myths , "twisted yarn"). There are several alternative names for the process, for example, "karyokinesis" (nuclear division), a term introduced by Schleicher in 1878, or "the same division", proposed by Weismann in 1887. However, the term "mitosis" is also used in a broad sense by some authors to refer to cariokinesis and cytokinesis together. Currently, the "categorical division" is more commonly used to refer to meiosis I.
Maps Mitosis
Phase
Overview
The main result of mitosis and cytokinesis is the transfer of stem cell genomes into two daughter cells. The genome is composed of a number of chromosomes - complexes of tightly coiled DNA containing important genetic information for proper cell function. Since every child cell produced must be genetically identical to the host cell, the stem cell must make copies of each chromosome before mitosis. This occurs during phase S of the interphase. The chromosomal duplication results in two identical sister chromatids are bound together by the cohesin protein at centromere .
When mitosis begins, the chromosomes condense and become visible. In some eukaryotes, such as animals, nuclear envelopes, which separate DNA from the cytoplasm, break down into small vesicles. Nucleolus, which makes the ribosome inside the cell, also disappears. The microtubule project from the ends of the cell, attaches to the centromere, and aligns the chromosomes centrally within the cell. The microtubules then contract to attract sister chromatids from each chromosome. Sister chromatids at this point are called daughter chromosomes . As the cell extends, the appropriate female chromosome is pulled toward the end of the cell and condenses to its maximum on the final anaphase. A new nuclear envelope is formed around a separate daughter's chromosome, which destroys to form the interfase nucleus.
During the development of mitosis, usually after the onset of anaphase, the cell may have cytokinesis. In animal cells, the cell membrane pinches in between two developing nuclei to produce two new cells. In plant cells, a cell plate is formed between two nuclei. Cytokinesis is not always the case; Coenocytic cells (a type of multinucleate cell) undergo mitosis without cytokinesis.
Interphase
The phase of mitosis is a relatively short period of cell cycle. This alternates with a longer interphase , in which the cell prepares for the process of cell division. The interphase is divided into three phases: G 1 (first gap), S (synthesis), and G 2 (second gap). During the three parts of the interphase, cells grow by producing proteins and cytoplasmic organelles. However, chromosomes are only replicated during phase S. Thus, the growing cell (G 1 ), continues to grow due to duplicate chromosomes (S), grows more and prepares for mitosis (G 2 ), and finally divide (M) before restarting the cycle. All of these phases in the cell cycle are highly regulated by cycloin, cyclin-dependent kinases, and other cell cycle proteins. Phases follow each other in tight sequences and there are "checkpoints" that give cell signals to continue from one phase to another. Cells can also temporarily or permanently leave the cell cycle and enter the phase G 0 to stop dividing. This can happen when cells become overcrowded (density dependent inhibition) or when they differentiate to carry out specific functions for the organism, as do the human heart muscle cells and neurons. Some G 0 cells have the ability to re-enter the cell cycle. Mitosis
Preprophase (plant cell)
In plant cells alone, prophase is preceded by the pre-prophase stage. In highly vacuolated plant cells, the nucleus must migrate to the cell center before mitosis can begin. This is achieved through the formation of a phragmosome, a transverse cytoplasm that divides the two cells along the plane of future cell division. In addition to the formation of phragmosome, preprophase is characterized by the formation of microtubule rings and actin filaments (called preprophase bands) beneath the plasma membrane around the equatorial plane of the future mitotic spindle. The band marks the position where the cell will eventually divide. High plant cells (such as flowering plants) do not have centrioles; instead, the microtubules form a spindle on the surface of the nucleus and then organized into spindles by the chromosomes themselves, after the nuclear envelope is damaged. The preprophase band disappears during the formation of the nuclear envelope and the formation of spindles in prometafase.
Profase
During the prophase, which occurs after the substrate G 2 , the cell prepares to divide by condensing its chromosomes strictly and initiating the formation of mitotic spindles. During interphase, the genetic material in the nucleus consists of chromatin which is packed loosely. At the beginning of the prophase, chromatin fibers condense into discrete chromosomes that are usually seen at high magnification through a light microscope. At this stage, the chromosome is long, thin and like a thread. Each chromosome has two chromatids. Both chromatids are joined in centromere.
Gene transcription stops during prophase and does not continue until anaphase is delayed to the initial G1 phase. Nucleolus also disappears during the initial prophase.
Close to the animal cell nucleus is a structure called centrosomes, consisting of a pair of centrioles surrounded by a loose collection of proteins. Centrosome is the coordination center of cell microtubules. A cell inherits a centrosome on cell division, which is duplicated by cells before the new mitotic phase begins, giving a pair of centrosomes. Both centrosomes polymerize tubulin to help form the microtubule spindle apparatus. The motor protein then pushes the centrosome along this microtubule to the opposite side of the cell. Although centrosomes help regulate microtubule assembly, they are not essential for the formation of spindle tools, as they are absent in plants, and are not absolutely necessary for animal cell mitosis.
Prometaphase
At the beginning of prometafase on animal cells, nuclear lamin phosphorylation causes the nuclear envelope to crumble into tiny membrane vesicles. When this happens, the microtubules invade the nuclear space. This is called open mitosis , and it occurs in some multicellular organisms. Fungi and some protists, such as algae or trichomonad, undergo a variation called closed mitosis in which the spindle forms inside the nucleus, or microtubules penetrate the complete nuclear envelope.
At the end of prometafase, the kinetokor microtubules begin to search for and attach to the chromosomal kinetokor. A kinetochore is a microtubular structure binding to proteins that form on the chromosomal centromere during the final prophase. A number of polar microtubules find and interact with the corresponding polar microtubules of the opposite centrosome to form the mitotic shaft. Although the structure and function of the kinetocor are not fully understood, it is known that it contains some form of molecular motors. When the microtubule is connected to the kinetocorch, the motor will be active, using energy from the ATP to "crawl" into the tube toward the originated centrosome. This motor activity, coupled with the polymerization and depolymerization of microtubules, provides the attractive force required to subsequently separate the two chromosat chromosomes.
Metaphase
Once the microtubules are and are attached to the kinetocorch in prometafase, the two centrosomes begin to pull the chromosome toward the opposite end of the cell. The resulting tension causes the chromosome to harmonize along the metaphase plates or the equatorial plane, the imaginary line located between two centrosomes (about the midline of the cell). To ensure the equalization of chromosomes at the end of mitosis, the metaphase check point assures that the kinetocor is firmly attached to the mitotic shaft and that the chromosomes are parallel along the metaphase plates. If the cell successfully passes the metaphase checkpoint, the cell will proceed to anaphase.
Anafase
During anaphase A , the cohesin that binds the chromatid brothers together is split, forming two identical female chromosomes. The shortening of the kinetocoroid microtubule attracts the newly formed daughter's chromosome to the opposite end of the cell. During anaphase B , polar microtubules push each other, causing the cells to elongate. At the end of the anaphase, the chromosome also achieves the maximum condensation level overall, to assist chromosome segregation and nuclear reshaping. In most animal cells, anaphase A precedes anaphase B, but some vertebrate eggs show the sequence of opposite events.
Telophase
Telophase (from the Greek word ????? meaning "end") is a reversal of prophase and prometafase events. In the telofase, polar microtubules continue to elongate, extending the cells even more. If the nuclear envelope has been damaged, the new nuclear envelope uses the old parent nuclear envelope vesicle membrane. New envelopes form around each set of separate daughter chromosomes (although the membrane does not close the centrosomes) and the nucleolus reappears. Both sets of chromosomes, now surrounded by a new nuclear membrane, begin to "relax" or decondense. Mitosis is complete. Each daughter nucleus has a set of identical chromosomes. Cell division may or may not occur at this point depending on the organism.
Cytokinesis
Cytokinesis is not a mitotic phase but a separate process, necessary to complete cell division. In animal cells, a pinch groove containing a contractile ring develops where the metaphase plate is used, pinching a separate core. In animal and plant cells, cell division is also driven by vesicles originating from the Golgi apparatus, which travels along microtubules to the center of the cell. In plants, these structures merge into the cellular plates at the center of the phragmoplast and develop into cell walls, separating the two nuclei. The phragmoplast is a typical microtubule structure for higher plants, while some green algae use microtubule array phycoplast during cytokinesis. Each child cell has a complete copy of the stem cell genome. The end of cytokinesis marks the end of the M-phase.
There are many cells in which mitosis and cytokinesis occur separately, forming single cells with many nuclei. The most important event of this is among mushrooms, slime molds, and coenocytic algae, but this phenomenon is found in various other organisms. Even in animals, cytokinesis and mitosis can occur independently, for example during certain stages of embryo development of the fly.
Function
Mitosis "function" or significance depends on the maintenance of the chromosome set; each formed cell receives the same chromosome in the composition and is equal in number to the stem cell chromosome.
Mitosis occurs under the following circumstances:
- Development and growth
- The number of cells in an organism increases with mitosis. This is the basis for the development of a multicellular body of a single cell, the zygote and also the base of multicellular body growth.
- Cell replacement
- In some parts of the body, such as the skin and gastrointestinal tract, cells are constantly removed and replaced with new ones. New cells are formed by mitosis and so are exact copies of the replaced cells. In the same way, red blood cells have a short lifespan (only about 4 months) and new red blood cells are formed by mitosis.
- Regeneration
- Some organisms can regenerate parts of the body. The production of new cells in such cases is achieved by mitosis. For example, starfish regenerates the missing arm through mitosis.
- Asexual reproduction
- Some organisms produce the same genetic offspring through asexual reproduction. For example, hydra reproduces asexually with buds. The cells on the hydra surface undergo mitosis and form a mass called buds. Mitosis continues in the stem cells and this grows into a new individual. The same division occurs during asexual reproduction or vegetative propagation in plants.
Variations
Forms of mitosis
The process of mitosis in cells of eukaryotic organisms follows a similar pattern, but with variations in three major details. Mitosis "closed" and "open" can be distinguished on the basis of the remaining or damaged nuclear envelope. The transitional form with partial degradation of the nuclear envelope is called mitosis "semiopen". With respect to the symmetry of the spindle apparatus during metaphase, the axial shape (centered) around the axial is referred to as "orthomitosis", distinguishing from the eccentric spindle "pleuromitosis", in which the mitotic apparatus has bilateral symmetry. Finally, the third criterion is the location of the central spindle in the case of closed pleuromitosis: "extranuclear" (spindles located in the cytoplasm) or "intranuclear" (in the nucleus).
Nuclear division occurs only in organism cells of the eukaryotic domain, because bacteria and archaea have no nuclei. In any eukaryotic supergroup, open-form mitosis can be found, as well as closed mitosis, except for Excavata, which exhibits exclusively closed mycosis. Here, the occurrence of mitosis in eukaryotes:
- Closed intranuclear Pleuromitosis is typical of Foraminifera, some Prasinomonadida, some Kinetoplastids, Oxymonadida, Haplosporidia, many fungi (chytrids, oomycetes, zygomycetes, ascomycetes), and some Radiolaria (Spumellaria and Acantharia ); it seems to be the most primitive type.
- closed extranuclear pleuromitosis occurs in Trichomonadida and Dinoflagellate.
- Closed orthomitosis is found among diatoms, ciliates, some microsporidians, unicellular yeasts, and some multicellular fungi.
- semiopen pleuromitosis is typical of most Apicomplexa.
- Semiopen orthomitosis occurs with variants in some amoebae (Lobosa) and some green flagella (eg, Raphidophyta or Volvox ).
- Open orthomitosis is typical in mammals and other Metazoa, and in terrestrial plants; but also occurs in some protists.
Errors and other variations
Mistakes can occur during mitosis, especially during early embryonic development in humans. Mistake errors can create aneuploid cells that have too little or too much of one or more chromosomes, a condition associated with cancer. Initial human embryos, cancer cells, infected or oxidized cells may also suffer from pathological division into three or more child cells (tripolar or multipolar mitosis), resulting in a severe error in their chromosomal complement.
In nondisjunction , sister chromatids fail to separate during anaphase. One daughter cell receives both chromatid sisters from the nondisjoining chromosome and the other cells do not accept. As a result, the former cell gets three copies of the chromosome, a condition known as trisomy , and the latter will have only one copy, a condition known as monosomy . Sometimes, when cells undergo nondisjunction, they fail to resolve the cytokinesis and retain both nuclei in one cell, producing nucleated cells.
Anafase lag occurs when the movement of one chromatid is retarded during anaphase. This may be due to the failure of the mitotic spindle to adhere properly to the chromosome. The remaining chromatids are excluded from both nuclei and disappear. Therefore, one of the child's cells will become a monosome for that chromosome.
Endoreduplication (or endoreplication) occurs when the chromosomes duplicate but the cell does not then divide. It produces polyploid cells or, if chromosomes replicate repeatedly, polytene chromosomes. Endoreduplication is found in many species and appears to be a normal part of development. Endomitosis is a variant of endoreduplication in which cells replicate their chromosomes during the S phase and enter, but before time ends, mitosis. Instead of being divided into two new daughter nuclei, the replicated chromosomes are retained within the original nucleus. The cells then re-enter G 1 and the S phase and replicate their chromosomes again. This can occur many times, increasing the number of chromosomes with each round of replication and endomitosis. Platelet producing megakariocytes have endomitosis during cell differentiation.
Amitosis in ciliates and in animal placental tissues results in the parental allele's random distribution.
Karyokinesis without cytokinesis derived many nucleated cells called coenocytes.
Related cell process
Cell rounding
In animal tissues, most cells rounded into an almost rounded shape during mitosis. In the epithelial and epidermis, efficient rounding processes correlate with the correct horizontal axis alignment and correct child cell placement. In addition, researchers have found that if rounding is strongly suppressed it can lead to spindle defects, particularly split poles and failure to efficiently capture chromosomes. Therefore, cell mitosis is considered to play a protective role in ensuring an accurate mitosis.
The rounding force is driven by the reorganization of F-actin and myosin (actomyosin) into the contractile homogeneous cortex cells that 1) strengthens the peripheral cells and 2) facilitates the formation of intracellular hydrostatic pressure (up to 10 times higher than interphase). The formation of intracellular pressure is very important in confinement, as will be important in network scenarios, where external forces must be generated to coalesce against adjacent cells and/or extracellular matrices. The generation of pressure depends on the nucleation of Formin-mediated F-actin and Rho kinase (ROCK) - myosin II contraction, both upstream by the RhoA and ECT2 signaling pathways through Cdk1 activity. Because of the importance of mitosis, the molecular components and cortical dynamics of actomyosin mitosis are active areas of research.
Mitotic recombination
Mitastated mitotic cells in the G1 phase of the cell cycle repair the damage of the recombinant DNA mainly by recombination between the homologous chromosomes. The mitotic cells which are irradiated in G2 phase repair such damage exclusively with brother-chromatid recombination. Mutations in genes that encode enzymes used in recombination cause cells to have increased sensitivity to be killed by various DNA-damaging agents. These findings suggest that mitotic recombination is an adaptation to repair DNA damage including potentially lethal.
Evolution
There are prokaryotic homologues of all the key molecules of eukaryotic mitosis (eg, actin, tubulin). Being a universal eukaryotic character, mitosis may appear at the base of eukaryotic trees. Because mitosis is less complex than meiosis, meiosis may appear after mitosis.
While in bacterial cell division, after DNA duplication, the two circular chromosomes attach to the special region of the cell membrane, eukaryotic mitosis is usually characterized by the presence of many linear chromosomes, the kinetocores attached to the spindle microtubules. In relation to the form of mitosis, closed intranuclear pleuromitosis appears to be the most primitive type, as it is more similar to bacterial division.
Gallery
The mitotic cells may be microscopically visualized by tainting them with antibodies and fluorescent dyes.
See also
- Aneuploidy
- Binary fission
- Chromosomal abnormalities
- Cytoskeleton
- Meiosis
- Mitogen
- Promotional Mitosis
- Mitotic tagging
- Motorcycle Protein
References
Further reading
External links
- Flash animations that compare Mitosis and Meiosis
- Khan Academy, college
- Studying Mitosis in a Cultivated Mammal Cell
- K-12 common class resources for Mitosis
- Cell-Cycle Ontology
- WormWeb.org: Interactive Visualization of C. elegans Cell Lineage - Visualize the whole tree of cell lineage and all cell divisions nematodes C. elegans
Source of the article : Wikipedia
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