Editing Mitosis (section)

====Prometaphase====
{{main|Prometaphase}}
At the beginning of prometaphase in animal cells, phosphorylation of [[lamin|nuclear lamins]] causes the [[nuclear envelope]] to disintegrate into small membrane [[Vesicle (biology and chemistry)|vesicles]]. As this happens, microtubules invade the nuclear space. This is called ''open mitosis'', and it occurs in some multicellular organisms. Fungi and some [[protist]]s, such as [[algae]] or [[trichomonad]]s, undergo a variation called ''closed mitosis'' where the spindle forms inside the nucleus, or the microtubules penetrate the intact nuclear envelope.<ref name="Heywood-1978"/><ref name="Ribeiro-2002"/>

In late prometaphase, ''kinetochore microtubules'' begin to search for and attach to chromosomal [[kinetochores]].<ref name="Chan-2005"/> A ''kinetochore'' is a [[protein]]aceous microtubule-binding structure that forms on the chromosomal centromere during late prophase.<ref name="Chan-2005"/><ref>{{cite journal | vauthors = Cheeseman IM, Desai A | title = Molecular architecture of the kinetochore-microtubule interface | journal = Nature Reviews. Molecular Cell Biology | volume = 9 | issue = 1 | pages = 33–46 | date = January 2008 | pmid = 18097444 | doi = 10.1038/nrm2310 }}</ref> A number of ''polar microtubules'' find and interact with corresponding polar microtubules from the opposite centrosome to form the mitotic spindle.<ref name="Winey-1995"/> Although the kinetochore structure and function are not fully understood, it is known that it contains some form of [[List of gene families#Motor proteins|molecular motor]].<ref name="Maiato-2004"/> When a microtubule connects with the kinetochore, the motor activates, using energy from [[Adenosine triphosphate|ATP]] to "crawl" up the tube toward the originating centrosome. This motor activity, coupled with polymerisation and depolymerisation of microtubules, provides the pulling force necessary to later separate the chromosome's two chromatids.<ref name="Maiato-2004"/>