Cell division: Difference between revisions

'''Cell division''' is the process by which a parent [[cell (biology)|cell]] divides into two daughter cells.<ref>{{Cite book|title=A dictionary of biology|date=2020 | vauthors = Martin EA, Hine R | publisher = Oxford University Press |isbn=9780199204625|edition=6th|location=Oxford|oclc=176818780}}</ref> Cell division usually occurs as part of a larger [[cell cycle]] in which the cell grows and replicates its chromosome(s) before dividing. In [[eukaryote]]s, 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 [[Haploidisation|haploid]] [[gamete]]s for sexual reproduction ([[meiosis]]), reducing the number of [[chromosome]]s from two of each type in the [[diploid]] parent cell to one of each type in the daughter cells.<ref name=":0">{{Cite book|title=Introduction to genetic analysis|date=2012| publisher=W.H. Freeman and Co.| vauthors = Griffiths AJ | isbn=9781429229432 |edition=10th |location=New York |oclc=698085201 }}</ref> Mitosis is a part of the [[cell cycle]], in which, replicated chromosomes are separated into two new [[Cell nucleus|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]], [[organelle]]s, and [[cell membrane]] of one cell into two new [[Cell (biology)|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.<ref>{{Cite web|title=10.2 The Cell Cycle – Biology 2e {{!}} OpenStax|url=https://openstax.org/books/biology-2e/pages/10-2-the-cell-cycle|access-date=2020-11-24|website=openstax.org|date=28 March 2018 |language=en}}</ref> To ensure proper progression through the cell cycle, DNA damage is detected and repaired at various checkpoints throughout the cycle. These checkpoints can halt progression through the cell cycle by inhibiting certain [[Cyclin-dependent kinase complex|cyclin-CDK complexes]]. Meiosis undergoes two divisions resulting in four haploid daughter cells. [[Homologous chromosome]]s 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. <ref>{{Citation |last=Gilbert |first=Scott F. |title=Meiosis |date=2000 |url=https://www.ncbi.nlm.nih.gov/books/NBK10019/ |work=Developmental Biology. 6th edition |access-date=2023-09-08 |publisher=Sinauer Associates |language=en}}</ref> 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.

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.<ref>{{Cite book|title=Cell division : theory, variants, and degradation | date=2010|url=https://www.worldcat.org/oclc/929650897|publisher=Nova Science Publishers|author1=Golitsin, Yuri N. |author2=Krylov, Mikhail C. C.|isbn=9781611225938|location=New York|pages=137|oclc=669515286}}</ref> A great deal of [[Cytoskeleton|cellular infrastructure]] is involved in ensuring consistency of genomic information among generations.<ref>{{Cite journal|last1=Fletcher|first1=Daniel A.|last2=Mullins|first2=R. Dyche|date=28 January 2010|title=Cell mechanics and the cytoskeleton|journal=Nature|volume=463|issue=7280|pages=485–492|doi=10.1038/nature08908|issn=0028-0836|pmc=2851742|pmid=20110992|bibcode=2010Natur.463..485F }}</ref><ref>{{Cite journal|last1=Li|first1=Shanwei|last2=Sun|first2=Tiantian|last3=Ren|first3=Haiyun|date=27 April 2015|title=The functions of the cytoskeleton and associated proteins during mitosis and cytokinesis in plant cells|journal=Frontiers in Plant Science|volume=6|pages=282|doi=10.3389/fpls.2015.00282|issn=1664-462X|pmc=4410512|pmid=25964792|doi-access=free}}</ref><ref>{{Cite journal|last1=Hohmann|first1=Tim|last2=Dehghani|first2=Faramarz|date=18 April 2019|title=The Cytoskeleton—A Complex Interacting Meshwork|journal=Cells|volume=8|issue=4|pages=362|doi=10.3390/cells8040362|issn=2073-4409|pmc=6523135|pmid=31003495|doi-access=free}}</ref>

Bacterial cell division happens through binary [[Fissionbinary (biology)|fission]] or sometimes 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.<ref>Cell Division: The Cycle of the Ring, Lawrence Rothfield and Sheryl Justice, [https://www.cell.com/fulltext/S0092-8674(00)81899-1#:~:text=The%20bacterial%20cell%20cycle%20can,to%20cytokinesis%20and%20cell%20separation. CELL], [https://doi.org/10.1016/S0092-8674(00)81899-1 DOI]</ref>

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 [[protist]]s (namely [[diatom]]s, [[dinoflagellate]]s, etc.) and [[Fungus|fungi]].{{citation needed|date=May 2024}}

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.{{citation needed|date=May 2024}}

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 [[chromatid]]s 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 [[Vestigiality|vestigial stage]] in higher plants), meiosis gives rise to [[spore]]s that [[Germination|germinate]] into the haploid vegetative phase (gametophyte). This kind of meiosis is called sporic meiosis.{{citation needed|date=May 2024}}

[[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 [[Kinetochore|kinetochoreskinetochore]]s 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.<ref>{{Cite web |title=Prometaphase – an overview {{!}} ScienceDirect Topics |url=https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/prometaphase |access-date=2023-11-21 |website=www.sciencedirect.com}}</ref> Prometaphase follows prophase and precedes metaphase.

[[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.<ref name=":3" /> 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.<ref>{{cite book | vauthors = Brooker AS, Berkowitz KM | title = Cell Cycle Control | chapter = The Roles of Cohesins in Mitosis, Meiosis, and Human Health and Disease | series = Methods in Molecular Biology | volume = 1170 | pages = 229–66 | date = 2014 | pmid = 24906316 | pmc = 4495907 | doi = 10.1007/978-1-4939-0888-2_11 | publisher = Springer | location = New York | isbn = 9781493908875 }}</ref> 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.<ref>{{Cite web|url=http://www.biology-pages.info/C/CellCycle.html|title=The Cell Cycle|website=www.biology-pages.info|access-date=2019-04-14}}</ref> As the sister chromatids are being pulled apart, the cell and plasma are elongated by non-kinetochore microtubules.<ref>{{cite book |title=Campbell Biology in Focus | location = Boston (Massachusetts) | publisher = Pearson | isbn = 978-0-321-81380-0 | date = 2014 | vauthors = Urry LA, Cain ML, Jackson RB, Wasserman SA, Minorsky PV, Reece JB }}</ref> Additionally, in this phase, the activation of the anaphase promoting complex through the association with [[CDH1 (gene)|Cdh-1]] begins the degradation of mitotic cyclins.<ref>{{Cite journal |last=Barford |first=David |date=2011-12-12 |title=Structural insights into anaphase-promoting complex function and mechanism |journal=Philosophical Transactions of the Royal Society B: Biological Sciences |language=en |volume=366 |issue=1584 |pages=3605–3624 |doi=10.1098/rstb.2011.0069 |pmid=22084387|pmc=3203452 }}</ref>

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.<ref>{{cnCite journal |last=Smith |first=Laurie G |date=MayDecember 20231999 |title=Divide and conquer: cytokinesis in plant cells |url=https://linkinghub.elsevier.com/retrieve/pii/S1369526699000229 |journal=Current Opinion in Plant Biology |language=en |volume=2 |issue=6 |pages=447–453 |doi=10.1016/S1369-5266(99)00022-9}}</ref>

In Fission yeast ([[Schizosaccharomyces pombe|''S. pombe'']]) the cytokinesis happens in G1 phase. <ref>The Cell, G.M. Cooper; ed 2 [https://www.ncbi.nlm.nih.gov/books/NBK9876/ NCBI bookshelf], The eukaryotic cell cycle, [https://www.ncbi.nlm.nih.gov/books/NBK9876/ Figure 14.7]</ref>

[[File:Kinetochore.jpg|thumb|200px|left|Image of the [[mitotic spindle]] in a human cell showing [[microtubule]]s in green, chromosomes (DNA) in blue, and kinetochores in red. {{cncitation needed|date=May 2023}}]]

DNA damage is detected and repaired at various points in the cell cycle. The [[Cell cycle checkpoint|G1/S checkpoint, G2/M checkpoint, and the checkpoint between metaphase and anaphase]] all monitor for DNA damage and halt cell division by inhibiting different cyclin-CDK complexes. The [[P53|p53 tumor-suppressor protein]] plays a crucial role at the G1/S checkpoint and the G2/M checkpoint. Activated p53 proteins result in the expression of many proteins that are important in cell cycle arrest, repair, and apoptosis. At the G1/S checkpoint, p53 acts to ensure that the cell is ready for DNA replication, while at the G2/M checkpoint p53 acts to ensure that the cells have properly duplicated their content before entering mitosis. <ref>{{Cite book |last1=Senturk |first1=Emir |last2=Manfredi |first2=James J. |title=P53 Protocols |date=2013 |chapter=p53 and Cell Cycle Effects After DNA Damage |series=Methods in Molecular Biology (Clifton, N.J.) |volume=962 |pages=49–61 |doi=10.1007/978-1-62703-236-0_4 |issn=1064-3745 |pmc=4712920 |pmid=23150436|isbn=978-1-62703-235-3 }}</ref>

If DNA is damaged, the cell can also alter the Akt pathway in which [[Bcl-2-associated death promoter|BAD]] is phosphorylated and dissociated from Bcl2, thus inhibiting apoptosis. If this pathway is altered by a loss of function mutation in Akt or Bcl2, then the cell with damaged DNA will be forced to undergo apoptosis. <ref>{{Cite journal |last1=Ruvolo |first1=P. P. |last2=Deng |first2=X. |last3=May |first3=W. S. |date=2001 |title=Phosphorylation of Bcl2 and regulation of apoptosis |url=https://www.nature.com/articles/2402090 |journal=Leukemia |language=en |volume=15 |issue=4 |pages=515–522 |doi=10.1038/sj.leu.2402090 |pmid=11368354 |s2cid=2079715 |issn=1476-5551}}</ref> If the DNA damage cannot be repaired, activated p53 can induce cell death by [[apoptosis]]. It can do so by activating the [[P53 upregulated modulator of apoptosis|p53 upregulated modulator of apoptosis (PUMA)]]. PUMA is a pro-apoptotic protein that rapidly induces apoptosis by inhibiting the anti-apoptotic [[Bcl-2]] family members.<ref>{{Cite journal |last1=Jabbour |first1=A. M. |last2=Heraud |first2=J. E. |last3=Daunt |first3=C. P. |last4=Kaufmann |first4=T. |last5=Sandow |first5=J. |last6=O'Reilly |first6=L. A. |last7=Callus |first7=B. A. |last8=Lopez |first8=A. |last9=Strasser |first9=A. |last10=Vaux |first10=D. L. |last11=Ekert |first11=P. G. |date=2009 |title=Puma indirectly activates Bax to cause apoptosis in the absence of Bid or Bim |journal=Cell Death & Differentiation |language=en |volume=16 |issue=4 |pages=555–563 |doi=10.1038/cdd.2008.179 |pmid=19079139 |issn=1476-5403|doi-access=free }}</ref>

[[Category:1835 in Germanythe German Confederation]]