Editing Prophase (section)

== Mitotic prophase ==
Prophase is the first stage of [[mitosis]] in [[Cell (biology)|animal cells]], and the second stage of [[mitosis]] in [[plant cell]]s.<ref name=":1">{{Cite book|title=Plant Physiology and Development| vauthors = Taiz L, Zeiger E, Moller IM, Murphy A |publisher=Sinauer Associates|year=2015|isbn=978-1-60535-255-8|location=Sunderland MA|pages=35–39}}</ref> At the start of prophase there are two identical copies of each [[chromosome]] in the cell due to replication in [[interphase]]. These copies are referred to as [[sister chromatids]] and are attached by [[DNA]] element called the [[centromere]].<ref name=":5">{{cite journal| vauthors = Zeng XL, Jiao MD, Wang XG, Song ZX, Rao S |date=2001|title=Electron microscopic studies on the Silver-stained Nucleolar Cycle of Physarum Polycephalum|url=http://www.jipb.net/pubsoft/content/2/2071/X000541(PS2).pdf|journal=Acta Botanica Sinica|volume=43|issue=7|pages=680–5|access-date=24 February 2015|archive-url=https://web.archive.org/web/20181001070430/http://www.jipb.net/pubsoft/content/2/2071/X000541(PS2).pdf|archive-date=2018-10-01}}</ref> The main events of prophase are: the condensation of [[chromosome]]s, the movement of the [[centrosome]]s, the formation of the [[Spindle apparatus|mitotic spindle]], and the beginning of [[Nucleolus|nucleoli]] break down.<ref name=":2">{{Cite book|title=Genetics From Genes to Genomes| vauthors = Hartwell LH, Hood L, Goldberg ML, Reynolds AE, Silver LM, Veres RC |publisher=McGraw-Hill|year=2008|isbn=978-0-07-284846-5|location=New York|pages=[https://archive.org/details/genetics00lela_0/page/90 90–103]|url-access=registration|url=https://archive.org/details/genetics00lela_0/page/90}}</ref>

=== Condensation of chromosomes ===
[[DNA]] that was [[DNA replication|replicated]] in [[interphase]] is condensed from DNA strands with lengths reaching 0.7 μm down to 
0.2-0.3 μm.<ref name=":2" /> This process employs the [[condensin]] complex.<ref name=":5" /> Condensed chromosomes consist of two [[sister chromatids]] joined at the [[centromere]].<ref name=":3">{{Cite book|title=Thompson & Thompson Genetics in Medicine| vauthors = Nussbaum RL, McInnes RR, Willard HF |publisher=Elsevier|year=2016|isbn=978-1-4377-0696-3|location=Philadelphia|pages=12–20}}</ref>

=== Movement of centrosomes ===
During prophase in [[Cell (biology)|animal cells]], [[centrosome]]s move far enough apart to be resolved using a [[light microscope]].<ref name=":2" /> [[Microtubule]] activity in each [[centrosome]] is increased due to recruitment of [[Tubulin#γ-Tubulin|γ-tubulin]]. Replicated [[centrosome]]s from [[interphase]] move apart towards opposite poles of the cell, powered by [[Motor protein|centrosome associated motor proteins]].<ref name=":4">{{Cite book|title=Essential Cell Biology| vauthors = Alberts B, Bray D, Hopkin K, Johnson A, Lewis J, Raff M, Roberts K, Walter P |publisher=Garland Science|year=2004|isbn=978-0-8153-3481-1|location=New York NY|pages=[https://archive.org/details/essentialcellbio00albe/page/639 639–658]|url=https://archive.org/details/essentialcellbio00albe/page/639}}</ref> Interdigitated interpolar [[microtubule]]s from each [[centrosome]] interact with each other, helping to move the [[centrosome]]s to opposite poles.<ref name=":4" /><ref name=":2" />

=== Formation of the mitotic spindle ===
[[Microtubule]]s involved in the [[interphase]] scaffolding break down as the replicated [[centrosome]]s separate.<ref name=":2" /> The movement of [[centrosome]]s to opposite poles is accompanied in [[Cell (biology)|animal cells]] by the organization of individual radial [[microtubule]] arrays (asters) by each centriole.<ref name=":4" /> Interpolar [[microtubule]]s from both [[centrosome]]s interact, joining the sets of [[microtubule]]s and forming the basic structure of the [[Spindle apparatus|mitotic spindle]].<ref name=":4" /> Plant cells do not have centrosomes and the [[chromosome]]s can [[Nucleation|nucleate]] [[microtubule]] assembly into the [[Spindle apparatus|mitotic apparatus]].<ref name=":4" /> In [[plant cell]]s, [[microtubule]]s gather at opposite poles and begin to form the [[spindle apparatus]] at locations called foci.<ref name=":1" /> The [[Spindle apparatus|mitotic spindle]] is of great importance in the process of [[mitosis]] and will eventually segregate the [[sister chromatids]] in [[metaphase]].<ref name=":2" />

=== Beginning of nucleoli breakdown ===
The [[Nucleolus|nucleoli]] begin to break down in prophase, resulting in the discontinuation of ribosome production.<ref name=":2" /> This indicates a redirection of cellular energy from general cellular metabolism to [[Cell division|cellular division]].<ref name=":2" /> The [[Nuclear membrane|nuclear envelope]] stays intact during this process.<ref name=":1" />