Editing Microtubule (section)

=== Centrosomes ===
[[File:Centriole3D.png|thumb|298x298px|A 3D diagram of a centriole. Each circle represents one microtubule. In total there are 27 microtubules organized into 9 bundles of 3.]]
The [[centrosome]] is the main MTOC ([[microtubule organizing center]]) of the cell during mitosis. Each centrosome is made up of two cylinders called [[centriole]]s, oriented at right angles to each other. The centriole is formed from 9 main microtubules, each having two partial microtubules attached to it. Each centriole is approximately 400&nbsp;nm long and around 200&nbsp;nm in circumference.<ref name="pmid10209087">{{Cite journal |vauthors=Marshall WF, Rosenbaum JL |date=March 1999 |title=Cell division: The renaissance of the centriole |journal=Current Biology |volume=9 |issue=6 |pages=R218–20 |bibcode=1999CBio....9.R218M |doi=10.1016/s0960-9822(99)80133-x |pmid=10209087 |s2cid=16951268 |doi-access=free}}</ref>

The centrosome is critical to mitosis as most microtubules involved in the process originate from the centrosome. The minus ends of each microtubule begin at the centrosome, while the plus ends radiate out in all directions. Thus the centrosome is also important in maintaining the polarity of microtubules during mitosis.<ref name="pmid9057082">{{Cite journal |vauthors=Pereira G, Schiebel E |date=February 1997 |title=Centrosome-microtubule nucleation |journal=Journal of Cell Science |volume=110 |issue=Pt 3 |pages=295–300 |doi=10.1242/jcs.110.3.295 |pmid=9057082}}</ref>

Most cells only have one centrosome for most of their cell cycle, however, right before mitosis, the centrosome duplicates, and the cell contains two centrosomes.<ref name="pmid11358861">{{Cite journal |vauthors=Hinchcliffe EH, Sluder G |date=May 2001 |title="It takes two to tango": understanding how centrosome duplication is regulated throughout the cell cycle |journal=Genes & Development |volume=15 |issue=10 |pages=1167–81 |doi=10.1101/gad.894001 |pmid=11358861 |doi-access=free}}</ref> Some of the microtubules that radiate from the centrosome grow directly away from the sister centrosome. These microtubules are called astral microtubules.  With the help of these astral microtubules the centrosomes move away from each other towards opposite sides of the cell. Once there, other types of microtubules necessary for mitosis, including interpolar microtubules and K-fibers can begin to form.<ref name="pmid28490474">{{Cite journal |vauthors=Forth S, Kapoor TM |date=June 2017 |title=The mechanics of microtubule networks in cell division |journal=The Journal of Cell Biology |volume=216 |issue=6 |pages=1525–1531 |doi=10.1083/jcb.201612064 |pmc=5461028 |pmid=28490474}}</ref>

A final important note about the centrosomes and microtubules during mitosis is that while the centrosome is the MTOC for the microtubules necessary for mitosis, research has shown that once the microtubules themselves are formed and in the correct place the centrosomes themselves are not needed for mitosis to occur.<ref>Khodjakov, A., Cole, R. W., Oakley, B. R. and Rieder, C. L. (2000). "Centrosome-independent mitotic spindle formation in vertebrates". ''Curr. Biol.'' 10, 59–67. doi:10.1016/S0960-9822(99)00276-6.</ref>