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it view history general what links here related changes upload file permanent link page information cite this page get shortened url switch to legacy parser print export download as pdf printable version in other projects wikimedia commons wikidata item appearance move to sidebar hide from wikipedia the free encyclopedia biological process not to be confused with cellular differentiation cell division in prokaryotes binary fission and eukaryotes mitosis and meiosis the thick lines are chromosomes and the thin blue lines are fibers pulling on the chromosomes and pushing the ends of the cell apart the cell cycle in eukaryotes i interphase m mitosis g 0 gap 0 g 1 gap 1 g 2 gap 2 s synthesis g 3 gap 3 cell division is the process by which a parent cell divides into two daughter cells 1 cell division usually occurs as part of a larger cell cycle in which the cell grows and replicates its chromosome s before dividing in eukaryotes there are two distinct types of cell division a vegetative division mitosis producing daughter cells genetically identical to the parent cell and a cell division that produces haploid gametes for sexual reproduction meiosis reducing the number of chromosomes from two of each type in the diploid parent cell to one of each type in the daughter cells 2 mitosis is a part of the cell cycle in which replicated chromosomes are separated into two new nuclei cell division gives rise to genetically identical cells in which the total number of chromosomes is maintained in general mitosis division of the nucleus is preceded by the s stage of interphase during which the dna replication occurs and is followed by telophase and cytokinesis which divides the cytoplasm organelles and cell membrane of one cell into two new cells containing roughly equal shares of these cellular components the different stages of mitosis all together define the m phase of an animal cell cycle the division of the mother cell into two genetically identical daughter cells 3 to ensure proper progression through the cell cycle dna damage is detected and repaired at various cell cycle checkpoints these checkpoints can halt progression through the cell cycle by inhibiting certain cyclin cdk complexes meiosis undergoes two divisions resulting in four haploid daughter cells homologous chromosomes are separated in the first division of meiosis such that each daughter cell has one copy of each chromosome these chromosomes have already been replicated and have two sister chromatids which are then separated during the second division of meiosis 4 both of these cell division cycles are used in the process of sexual reproduction at some point in their life cycle both are believed to be present in the last eukaryotic common ancestor prokaryotes bacteria and archaea usually undergo a vegetative cell division known as binary fission where their genetic material is segregated equally into two daughter cells but there are alternative manners of division such as budding that have been observed all cell divisions regardless of organism are preceded by a single round of dna replication for simple unicellular microorganisms such as the amoeba one cell division is equivalent to reproduction an entire new organism is created on a larger scale mitotic cell division can create progeny from multicellular organisms such as plants that grow from cuttings mitotic cell division enables sexually reproducing organisms to develop from the one celled zygote which itself is produced by fusion of two gametes each having been produced by meiotic cell division 5 6 after growth from the zygote to the adult cell division by mitosis allows for continual construction and repair of the organism 7 the human body experiences about 10 quadrillion cell divisions in a lifetime 8 the primary concern of cell division is the maintenance of the original cell s genome before division can occur the genomic information that is stored in chromosomes must be replicated and the duplicated genome must be cleanly divided between progeny cells 9 a great deal of cellular infrastructure is involved in ensuring consistency of genomic information among generations 10 11 12 in bacteria edit divisome and elongasome complexes responsible for peptidoglycan synthesis during lateral cell wall growth and division 13 bacterial cell division happens through binary fission or through budding the divisome is a protein complex in bacteria that is responsible for cell division constriction of inner and outer membranes during division and remodeling of the peptidoglycan cell wall at the division site a tubulin like protein ftsz plays a critical role in formation of a contractile ring for the cell division 14 in eukaryotes edit see also alternation of generations cell division in eukaryotes is more complicated than in prokaryotes if the chromosomal number is reduced eukaryotic cell division is classified as meiosis reductional division if the chromosomal number is not reduced eukaryotic cell division is classified as mitosis equational division a primitive form of cell division called amitosis also exists the amitotic or mitotic cell divisions are more atypical and diverse among the various groups of organisms such as protists namely diatoms dinoflagellates etc and fungi 15 forms of mitosis of karyokinesis step in eukaryotes closed intranuclear pleuromitosis closed extranuclear pleuromitosis closed orthomitosis semiopen pleuromitosis semiopen orthomitosis open orthomitosis in the mitotic metaphase see below typically the chromosomes each containing 2 sister chromatids that developed during replication in the s phase of interphase align themselves on the metaphase plate then the sister chromatids split and are distributed between two daughter cells 16 in meiosis i the homologous chromosomes are paired before being separated and distributed between two daughter cells on the other hand meiosis ii is similar to mitosis the chromatids are separated and distributed in the same way in humans other higher animals and many other organisms the process of meiosis is called gametic meiosis during which meiosis produces four gametes whereas in several other groups of organisms especially in plants observable during meiosis in lower plants but during the vestigial stage in higher plants meiosis gives rise to spores that germinate into the haploid vegetative phase gametophyte this kind of meiosis is called sporic meiosis 17 phases of eukaryotic cell division edit the phases ordered counter clockwise of cell division mitosis and the cell cycle in animal cells interphase edit interphase is the process through which a cell must go before mitosis meiosis and cytokinesis 18 interphase consists of three main phases g 1 s and g 2 g 1 is a time of growth for the cell where specialized cellular functions occur in order to prepare the cell for dna replication 19 there are checkpoints during interphase that allow the cell to either advance or halt further development one of the checkpoint is between g 1 and s the purpose for this checkpoint is to check for appropriate cell size and any dna damage the second check point is in the g 2 phase this checkpoint also checks for cell size but also the dna replication the last check point is located at the site of metaphase where it checks that the chromosomes are correctly connected to the mitotic spindles 20 in s phase the chromosomes are replicated in order for the genetic content to be maintained 21 during g 2 the cell undergoes the final stages of growth before it enters the m phase where spindles are synthesized the m phase can be either mitosis or meiosis depending on the type of cell germ cells or gametes undergo meiosis while somatic cells will undergo mitosis after the cell proceeds successfully through the m phase it may then undergo cell division through cytokinesis the control of each checkpoint is controlled by cyclin and cyclin dependent kinases the progression of interphase is the result of the increased amount of cyclin as the amount of cyclin increases more and more cyclin dependent kinases attach to cyclin signaling the cell further into interphase at the peak of the cyclin attached to the cyclin dependent kinases this system pushes the cell out of interphase and into the m phase where mitosis meiosis and cytokinesis occur 22 there are three transition checkpoints the cell has to go through before entering the m phase the most important being the g 1 s transition checkpoint if the cell does not pass this checkpoint it results in the cell exiting the cell cycle 23 prophase edit prophase is the first stage of division the nuclear envelope begins to be broken down in this stage long strands of chromatin condense to form shorter more visible strands called chromosomes the nucleolus disappears and the mitotic spindle begins to assemble from the two centrosomes 24 microtubules associated with the alignment and separation of chromosomes are referred to as the spindle and spindle fibers chromosomes will also be visible under a microscope and will be connected at the centromere during this condensation and alignment period in meiosis the homologous chromosomes undergo a break in their double stranded dna at the same locations followed by a recombination of the now fragmented parental dna strands into non parental combinations known as crossing over 25 this process is evidenced to be caused in a large part by the highly conserved spo11 protein through a mechanism similar to that seen with topoisomerase in dna replication and transcription 26 prometaphase edit prometaphase is the second stage of cell division this stage begins with the complete breakdown of the nuclear envelope which exposes various structures to the cytoplasm this breakdown then allows the spindle apparatus growing from the centrosome to attach to the kinetochores on the sister chromatids stable attachment of the spindle apparatus to the kinetochores on the sister chromatids will ensure error free chromosome segregation during anaphase 27 prometaphase follows prophase and precedes metaphase metaphase edit in metaphase the centromeres of the chromosomes align themselves on the metaphase plate or equatorial plate an imaginary line that is at equal distances from the two centrosome poles and held together by complexes known as cohesins chromosomes line up in the middle of the cell by microtubule organizing centers mtocs pushing and pulling on centromeres of both chromatids thereby causing the chromosome to move to the center at this point the chromosomes are still condensing and are currently one step away from being the most coiled and condensed they will be and the spindle fibers have already connected to the kinetochores 28 during this phase all the microtubules with the exception of the kinetochores are in a state of instability promoting their progression toward anaphase 29 at this point the chromosomes are ready to split into opposite poles of the cell toward the spindle to which they are connected 30 anaphase edit anaphase is a very short stage of the cell cycle and it occurs after the chromosomes align at the mitotic plate kinetochores emit anaphase inhibition signals until their attachment to the mitotic spindle once the final chromosome is properly aligned and attached the final signal dissipates and triggers the abrupt shift to anaphase 29 this abrupt shift is caused by the activation of the anaphase promoting complex and its function of tagging degradation of proteins important toward the metaphase anaphase transition one of these proteins that is broken down is securin which through its breakdown releases the enzyme separase that cleaves the cohesin rings holding together the sister chromatids thereby leading to the chromosomes separating 31 after the chromosomes line up in the middle of the cell the spindle fibers will pull them apart the chromosomes are split apart while the sister chromatids move to opposite sides of the cell 32 as the sister chromatids are being pulled apart the cell and plasma are elongated by non kinetochore microtubules 33 additionally in this phase the activation of the anaphase promoting complex through the association with cdh 1 begins the degradation of mitotic cyclins 34 telophase edit telophase is the last stage of the cell cycle in which a cleavage furrow splits the cells cytoplasm cytokinesis and chromatin this occurs through the synthesis of a new nuclear envelope that forms around the chromatin gathered at each pole the nucleolus reforms as the chromatin reverts back to the loose state it possessed during interphase 35 36 the division of the cellular contents is not always equal and can vary by cell type as seen with oocyte formation where one of the four daughter cells possess the majority of the duckling 37 cytokinesis edit the last stage of the cell division process is cytokinesis in this stage there is a cytoplasmic division that occurs at the end of either mitosis or meiosis at this stage there is a resulting irreversible separation leading to two daughter cells cell division plays an important role in determining the fate of the cell this is due to there being the possibility of an asymmetric division this as a result leads to cytokinesis producing unequal daughter cells containing completely different amounts or concentrations of fate determining molecules 38 in animals the cytokinesis ends with formation of a contractile ring and thereafter a cleavage but in plants it happen differently at first a cell plate is formed and then a cell wall develops between the two daughter cells 39 in fission yeast s pombe the cytokinesis happens in g1 phase 40 variants edit image of the mitotic spindle in a human cell showing microtubules in green chromosomes dna in blue and kinetochores in red citation needed cells are broadly classified into two main categories simple non nucleated prokaryotic cells and complex nucleated eukaryotic cells due to their structural differences eukaryotic and prokaryotic cells do not divide in the same way also the pattern of cell division that transforms eukaryotic stem cells into gametes sperm cells in males or egg cells in females termed meiosis is different from that of the division of somatic cells in the body cell division over 42 hours the cells were directly imaged in the cell culture vessel using non invasive quantitative phase contrast time lapse microscopy 41 in 2022 scientists discovered a new type of cell division called asynthetic fission found in the squamous epithelial cells in the epidermis of juvenile zebrafish when juvenile zebrafish are growing skin cells must quickly cover the rapidly increasing surface area of the zebrafish these skin cells divide without duplicating their dna the s phase of mitosis causing up to 50 of the cells to have a reduced genome size these cells are later replaced by cells with a standard amount of dna scientists expect to find this type of division in other vertebrates 42 dna damage repair in the cell cycl...
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