Editing Centrosome (section)

==Functions==
{{Further|Centrosome cycle}}
[[Image:Molly Sheehan Wikipedia 1.jpg|right|thumb|300px|Role of the centrosome in cell cycle progression]]
 
Centrosomes are associated with the [[nuclear membrane]] during the [[prophase]] stage of the cell cycle. During [[mitosis]], the nuclear membrane breaks down, and the centrosome-nucleated [[microtubule]]s can interact with the [[chromosome]]s 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]].<ref name=rieder/>

The centrosome is copied only once per [[cell cycle]], so that each daughter cell inherits one centrosome, containing two structures called centrioles. 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 then 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 [[semiconservative replication|semiconservative]] nature of the process and the action of [[CDK2]] as a regulator of the process.<ref>{{Cite journal
| pmid = 11371338
| date=May 2001 | first = T.
| title = Centrosome duplication. A centriolar pas de deux
| volume = 105
| issue = 4
| pages = 417–420
| issn = 0092-8674
| journal = Cell
| doi = 10.1016/S0092-8674(01)00366-X
| author1=Stearns | s2cid=1622118 | doi-access = free
}}</ref> But the processes are essentially different in that centrosome doubling does not occur by template reading and assembly. The mother centriole just aids in the accumulation of materials required for the assembly of the daughter centriole.<ref>{{Cite journal| first1 = A.| last1 = Rodrigues-martins | first2 = M.| first3 = G.| first4 = D. M.| first5 = M.
| journal = Science
| last5 = Bettencourt-dias
| last2 = Riparbelli
| last4 = Glover
| last3 = Callaini
| s2cid = 6965044 | title = Revisiting the Role of the Mother Centriole in Centriole Biogenesis
| volume = 316
| pages = 1046–50
| year = 2007 
| doi = 10.1126/science.1142950
| pmid =  17463247
| issue =  5827
|bibcode = 2007Sci...316.1046R | hdl = 10400.7/955 | url = https://resolver.caltech.edu/CaltechAUTHORS:20201002-140639487 | hdl-access = free
}}</ref>

[[Image:Cytokinesis-electron-micrograph.jpg|thumb|right|400px|Centrosome (shown by arrow) next to nucleus]]

Centrioles, however, 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.<ref name="pmid16814722">{{Cite journal
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| last7 = Raff | first1 = R.
| last2 = Lau | first2 = J. | first3 = T.
| last5 = Woods
| last4 = Gardiol | first4 = A. | first5 = G.
| last1 = Basto | first6 = A. | first7 = W.
| title = Flies without centrioles
| journal = Cell
| last6 = Khodjakov
| volume = 125
| issue = 7
| pages = 1375–1386
| date=Jun 2006 | issn = 0092-8674
| pmid = 16814722
| doi = 10.1016/j.cell.2006.05.025
| s2cid = 2080684 | doi-access = free
}}</ref> In the absence of the centrioles, the microtubules of the spindle are focused by [[molecular motor|motor]]s, allowing the formation of a bipolar spindle. Many cells can completely undergo interphase without centrioles.<ref name=rieder/>

Unlike centrioles, centrosomes are required for survival of the organism. Cells without centrosomes lack radial arrays of [[astral microtubules]]. They are also defective in spindle positioning and in the ability to establish a central localization site in cytokinesis. The function of centrosomes in this context is hypothesized to ensure the fidelity of [[cell division]], because it greatly increases the efficacy. Some cell types arrest in the following cell cycle when centrosomes are absent. This is not a universal phenomenon.

When the nematode ''[[Caenorhabditis elegans|C. elegans]]'' egg is fertilized, the sperm delivers a pair of centrioles. These centrioles will form the centrosomes, which will direct the first cell division of the [[zygote]], and this will determine its polarity. It's not yet clear whether the role of the centrosome in polarity determination is microtubule-dependent or independent.

In human reproduction, the [[sperm]] supplies the centriole that creates the centrosome and microtubule system of the zygote.<ref>{{Cite book|chapter=The biology of fertilization in humans|editor=Patrizio, Pasquale|title=A color atlas for human assisted reproduction: laboratory and clinical insights|publisher=Lippincott Williams & Wilkins|year=2003|isbn=978-0-7817-3769-2|page=3|chapter-url=https://books.google.com/books?id=2SBoQ8H-KMIC&pg=PA3|author1=Hewitson, Laura|author2=Schatten, Gerald P.|name-list-style=amp|access-date=2013-11-09|display-editors=etal|archive-date=2024-03-21|archive-url=https://web.archive.org/web/20240321115533/https://books.google.com/books?id=2SBoQ8H-KMIC&pg=PA3#v=onepage&q&f=false|url-status=live}}</ref>