Cell division 36869 225774082 2008-07-15T09:57:30Z 120.28.135.213 /* Prokaryotic cells */ {{Nofootnotes||date=August 2007}} '''Cell division''' is a process by which a [[cell (biology)|cell]], called the parent cell, divides into two or more cells, called ''daughter cells''. Cell division is usually a small segment of a larger [[cell cycle]]. This type of cell division is known as mitosis, and leaves the daughter cell capable of dividing again. In another type of cell division present only in eukaryotes, called [[meiosis]], a cell is permanently transformed into a gamete and cannot divide again until fertilization. For simple [[unicellular organism]]s such as the [[Amoeba]], one cell division is equivalent to [[vegetative reproduction|reproduces]]-- 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. Cell division also enables [[sexual reproduction|sexually reproducing]] organisms to develop from the one-celled [[zygote]], which itself was produced by cell division from [[gamete]]s. And after growth, cell division allows for continual renewal and repair of the organism.<ref>{{cite book | last = Maton | first = Anthea | authorlink = | coauthors = Hopkins, Jean Johnson, Susan LaHart, David, Quon Warner, David, Wright, Jill D | title = Cells: Building Blocks of Life | publisher = Prentice Hall | date = 1997 | location = New Jersey | pages = 70-74 | url = | doi = | id = | isbn = 0-13423476-6 }}</ref> A human being's body experiences about 10,000 trillion cell divisions in a lifetime.<ref>{{Citation | last = Quammen | first = David | author-link = | last2 = | first2 = | author2-link = | title = Contagious cancer: The evolution of a killer | journal = Harper's | volume = 316 | issue = 1895 | pages = 42 | date = April 2008 | year = 2008 | url = | doi = | id = }}.</ref> The primary concern of cell division is the maintenance of the original cell's [[genome]]. Before division can occur, the genomic information which is stored in [[chromosomes]] must be replicated, and the duplicated genome separated cleanly between cells. A great deal of cellular infrastructure is involved in keeping genomic information consistent between "generations". ==Variants== [[Image:Three cell growth types.png|thumb|300px|right|Three types of cell division]] '''Cells''' are classified into two categories: simple, non-nucleated [[prokaryote|prokaryotic]] cells, and complex, nucleated [[eukaryote|eukaryotic]] cells. By dint of their structural differences, '''eukaryotic''' and '''prokaryotic''' cells do not divide in the same way. Furthermore, the pattern of cell division that transforms eukaryotic [[stem cell]]s into gametes ([[sperm]] in males or [[ova]] in females) is different from that of eukaryotic [[somatic]] (non-germ) cells. ===Prokaryotic cells=== {{main|binary fission}} ===Eukaryotic cells=== [[Eukaryotic]] cells consist of cell [[membrane]], [[organelles]] which represent the functional components for storage, [[excretion]], [[digestion]] and [[nucleus]] (centre of the cell), it contains all the vital information needed by the cell or the whole organism to function, grow and [[reproduce]]. Eukaryotic cells are found in humans, plants and animals, also [[algae]], and [[protozoa]]. Eukaryotic cells have both a cellular membrane and a nuclear membrane. Eukaryotic [[genome]] is more complex than that of [[prokaryotes]] and distributed among multiple [[chromosomes]]. * '''[[Mitosis]]''': The division of the parent nucleus into two daughter nuclei, separating the duplicated genome into two sets, each identical to the parent cell's genome. * '''[[Cytokinesis]]''': The pinching and division of the cell membrane and [[cytoplasm]], separating the recently divided nuclei, the organelles, and other cellular components. * '''[[Meiosis]]''': The division of the nucleus in sex cells that reduces the [[diploid]] number of chromosomes to a [[haploid]] number in order to facilitate sexual reproduction. Examples of cell division in multicellular eukariotic organisms include repair, growth, and development. An injury or wound is healed when the cells exposed by the injury divide at an excellerated rate until they come into contact with other cells. After this the cells return to a more typical division rate. Cell division causes an organism to grow as long as the rate of cell division exceeds normal cell death. As cells divide and become more numerous they are located in more diverse physical and chemical environments. These variations in local conditions influence the cells to alter gene expression causing the cells to differentiate and become more specialized allowing an organism to develop. ==Degradation== Multicellular organisms replace worn-out cells through cell division. In some animals, however, cell division eventually halts. In [[human]]s this occurs on average, after 52 divisions, known as the [[Hayflick limit]]. The cell is then referred to as [[Senescence|senescent]]. Senescent cells deteriorate and die, causing the body to age.{{Fact|date=June 2008}} Cells stop dividing because the [[telomere]]s, protective bits of DNA on the end of a [[chromosome]], become shorter with each division and eventually can no longer protect the chromosome.{{Fact|date=June 2008}} [[Cancer]] cells, on the other hand, are immortal. An [[enzyme]] called [[telomerase]], present in large quantites in cancerous cells, rebuilds the telomeres, allowing division to continue indefinitely. ==See also== * [[Cell cycle]] * [[Mitosis]] * [[Meiosis]] * [[Binary fission]] * [[Cell growth]] * [[Constantly dividing cells]] ==References== # Morgan DO. (2007) "The Cell Cycle: Principles of Control" London: New Science Press. # J.M.Turner ''Fetus into Man'' (1978, 1989). Harvard University Press. ISBN 0-674-30692-9 ===Other references=== <div class='references-small'> <references/> </div> ==External links== * [http://www.pbs.org/wgbh/nova/baby/divide.html How Cells Divide: Mitosis vs. Meiosis] * The [http://cellimages.ascb.org/u?/p4041coll11,88 Mitosis and Cell Cycle Control Section] from the [http://cellimages.ascb.org/cdm4/browse.php?CISOROOT=/p4041coll11 ''Landmark Papers in Cell Biology''] (Gall JG, McIntosh JR, eds.) contains commentaries on and links to seminal research papers on mitosis and cell division. Published online in the [http://cellimages.ascb.org Image & Video Library] of [http://www.ascb.org The American Society for Cell Biology] *The [http://cellimages.ascb.org Image & Video Library] of [http://www.ascb.org The American Society for Cell Biology] contains many videos showing mitosis and cell division. *Videos of the first cell divisions in [[Xenopus laevis]] embryos ([http://www.blackwell-synergy.com/doi/suppl/10.1111/j.1432-0436.2006.00114.x/suppl_file/Movie+S1.mov side view] and [http://www.blackwell-synergy.com/doi/suppl/10.1111/j.1432-0436.2006.00114.x/suppl_file/Movie+S2.mov top view]), acquired by [[MRI]] ([http://dx.doi.org/10.1111/j.1432-0436.2006.00114.x DOI of paper]) * [http://www.alpine-plants-jp.com/himitunohanazono/ebine_himitu_3.htm Images : ''Calanthe discolor'' Lindl.] - Flavon's Secret Flower Garden {{Cell cycle}} [[Category:Cell cycle]] [[Category:Cellular processes]] [[ar:انقسام خلوي]] [[cs:Buněčné dělení]] [[da:Celledeling]] [[de:Zellteilung]] [[es:División celular]] [[fr:Division cellulaire]] [[ko:세포 분열]] [[it:Divisione cellulare]] [[he:רבייה תאית]] [[lt:Ląstelės dauginimasis]] [[mk:Делба на клетките]] [[ja:細胞分裂]] [[no:Celledeling]] [[nn:Celledeling]] [[pl:Podział komórki]] [[pt:Divisão celular]] [[simple:Cell division]] [[sk:Bunkové delenie]] [[sr:Ћелијска деоба]] [[fi:Solunjakautuminen]] [[sv:Celldelning]] [[th:การแบ่งเซลล์]] [[tr:Hücre bölünmesi]] [[uk:Поділ клітини]] [[zh:细胞分裂]]