Editing Mitosis (section)

====Prophase====
{{main|Prophase}}
[[File:CONDENSING CHROMOSOMES 2.jpg|thumb|left|Interphase nucleus (left), condensing chromosomes (middle) and condensed chromosomes (right)]]

[[File:Prophase diagram.svg|thumb|[[Prophase]] during mitosis]]

During prophase, which occurs after G<sub>2</sub> interphase, the cell prepares to divide by tightly condensing its chromosomes and initiating mitotic spindle formation. During interphase, the genetic material in the nucleus consists of loosely packed [[chromatin]]. At the onset of prophase, chromatin fibers condense into discrete chromosomes that are typically visible at high magnification through a [[light microscope]]. In this stage, chromosomes are long, thin, and thread-like. Each chromosome has two chromatids. The two chromatids are joined at the centromere.

[[Gene transcription]] ceases during prophase and does not resume until late anaphase to early G<sub>1</sub> phase.<ref>{{cite journal | vauthors = Prasanth KV, Sacco-Bubulya PA, Prasanth SG, Spector DL | title = Sequential entry of components of the gene expression machinery into daughter nuclei | journal = Molecular Biology of the Cell | volume = 14 | issue = 3 | pages = 1043–57 | date = March 2003 | pmid = 12631722 | pmc = 151578 | doi = 10.1091/mbc.E02-10-0669 }}</ref><ref>
{{cite journal | vauthors = Kadauke S, Blobel GA | title = Mitotic bookmarking by transcription factors | journal = Epigenetics & Chromatin | volume = 6 | issue = 1 | pages = 6 | date = April 2013 | pmid = 23547918 | pmc = 3621617 | doi = 10.1186/1756-8935-6-6 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Prescott DM, Bender MA | title = Synthesis of RNA and protein during mitosis in mammalian tissue culture cells | journal = Experimental Cell Research | volume = 26 | issue = 2 | pages = 260–8 | date = March 1962 | pmid = 14488623 | doi = 10.1016/0014-4827(62)90176-3 }}</ref> The [[nucleolus]] also disappears during early prophase.<ref>{{cite book | vauthors = Olson MO | date=2011 |title=The Nucleolus |volume=15 of Protein Reviews |location=Berlin |publisher=Springer Science & Business Media |page=15 |isbn=9781461405146 }}</ref>

Close to the nucleus of an animal cell are structures called [[centrosome]]s, consisting of a pair of [[centriole]]s surrounded by a [[Pericentriolar material|loose collection of proteins]]. The centrosome is the coordinating center for the cell's [[microtubule]]s. A cell inherits a single centrosome at cell division, which is [[Centrosome cycle|duplicated by the cell]] before a new round of mitosis begins, giving a pair of centrosomes. The two centrosomes polymerize [[tubulin]] to help form a [[spindle apparatus|microtubule spindle apparatus]]. [[Motor proteins]] then push the centrosomes along these microtubules to opposite sides of the cell. Although centrosomes help organize microtubule assembly, they are not essential for the formation of the spindle apparatus, since they are absent from plants,<ref name="Lloyd-2006"/> and are not absolutely required for animal cell mitosis.<ref name="Basto-2006">{{cite journal | vauthors = Basto R, Lau J, Vinogradova T, Gardiol A, Woods CG, Khodjakov A, Raff JW | title = Flies without centrioles | journal = Cell | volume = 125 | issue = 7 | pages = 1375–86 | date = June 2006 | pmid = 16814722 | doi = 10.1016/j.cell.2006.05.025 | doi-access = free }}</ref>