Editing Anaphase

{{Short description|Stage of a cell division}}{{Distinguish|Anaphase I|Anaphase II}}
[[File:Anaphase.svg|thumb|300px]]
[[Image:Anaphase IF.jpg|thumb|right|300px|A cell during anaphase. Microtubules are visible in green.]]
[[File:Stages of late M phase in a vertebrate cell.svg|thumb|right|Stages of late M phase in a vertebrate cell]]

'''Anaphase''' ({{etymology|grc|''[[wikt:ἀνα-|ἀνα-]]'' ([[wikt:ana-|ana-]])|back, backward||''[[wikt:φάσις|φάσις]]'' (phásis)|appearance}}) is the stage of [[mitosis]] after the process of [[metaphase]], when replicated [[chromosome]]s are split and the newly-copied chromosomes (daughter [[chromatid]]s) are moved to opposite poles of the cell. [[Chromosome]]s also reach their overall maximum  condensation in late anaphase, to help [[chromosome]] segregation and the re-formation of the nucleus.<ref>{{cite web|title=Chromosome condensation through mitosis|url=https://www.sciencedaily.com/releases/2007/06/070611122252.htm|website=Science Daily|access-date=12 June 2007}}</ref>

Anaphase starts when the [[anaphase promoting complex]] marks an [[Chaperone (protein)|inhibitory chaperone]] called [[securin]] for destruction by [[Ubiquitin|ubiquitylating]] it. Securin is a protein which inhibits a [[protease]] known as [[separase]]. The destruction of securin unleashes separase which then breaks down [[cohesin]], a protein responsible for holding sister chromatids together.<ref name="Kimball's Biology Pages">{{cite web|url=http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellCycle.html|title=The Cell Cycle|publisher=Kimball's Biology Pages|access-date=9 December 2012|archive-url=https://web.archive.org/web/20121119134405/http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellCycle.html|archive-date=2012-11-19|url-status=dead}}</ref>

At this point, three subclasses of [[microtubule]] unique to mitosis are involved in creating the forces necessary to separate the chromatids: kinetochore microtubules, interpolar microtubules, and [[Aster_(cell_biology)#Astral_microtubules|astral]] microtubules.

The centromeres are split, and the sister chromatids are pulled toward the poles by kinetochore microtubules. They take on a V-shape or Y-shape as they are pulled to either pole.

While the chromosomes are drawn to each side of the cell, interpolar microtubules and astral microtubules generate forces that stretch the cell into an oval.<ref name="NCBI">{{cite journal | vauthors = Hickson GR, Echard A, O'Farrell PH | title = Rho-kinase controls cell shape changes during cytokinesis | journal = Current Biology | volume = 16 | issue = 4 | pages = 359–70 | date = February 2006 | pmid = 16488869 | pmc = 1525334 | doi = 10.1016/j.cub.2005.12.043 }}</ref>

Once anaphase is complete, the cell moves into [[telophase]].<ref>{{cite journal | vauthors = Schafer KA | title = The cell cycle: a review | journal = Veterinary Pathology | volume = 35 | issue = 6 | pages = 461–78 | date = November 1998 | pmid = 9823588 | doi = 10.1177/030098589803500601 | s2cid = 43902779 }}</ref>

== Phases ==
Anaphase is characterized by two distinct motions. The first of these, anaphase A, moves chromosomes to either pole of a dividing cell (marked by [[centrosome]]s, from which mitotic microtubules are generated and organised). The movement for this is primarily generated by the action of kinetochores, and a subclass of microtubule called kinetochore microtubules.

The second motion, anaphase B, involves the separation of these poles from each other. The movement for this is primarily generated by the action of interpolar microtubules and astral microtubules.

=== Anaphase A ===
A combination of different forces have been observed acting on chromatids in anaphase A, but the primary force is exerted centrally. Microtubules attach to the midpoint of chromosomes (the [[centromere]]) via protein complexes ([[kinetochore]]s). The attached microtubules depolymerise and shorten, which together with motor proteins creates movement that pulls chromosomes towards centrosomes located at each pole of the cell.<ref name=":0">{{cite journal | vauthors = Asbury CL | title = Anaphase A: Disassembling Microtubules Move Chromosomes toward Spindle Poles | journal = Biology | volume = 6 | issue = 1 | pages = 15 | date = February 2017 | pmid = 28218660 | pmc = 5372008 | doi = 10.3390/biology6010015 | doi-access = free }}</ref>

=== Anaphase B ===
The second part of anaphase is driven by its own distinct mechanisms. Force is generated by several actions. Interpolar microtubules begin at each centrosome and join at the equator of the dividing cell. They push against one another, causing each centrosome to move further apart. Meanwhile, astral microtubules begin at each centrosome and join with the cell membrane. This allows them to pull each centrosome closer to the cell membrane. Movement created by these microtubules is generated by a combination of microtubule growth or shrinking, and by motor proteins such as [[dynein]]s or [[kinesin]]s.<ref>{{cite journal | vauthors = Scholey JM, Civelekoglu-Scholey G, Brust-Mascher I | title = Anaphase B | journal = Biology | volume = 5 | issue = 4 | pages = 51 | date = December 2016 | pmid = 27941648 | pmc = 5192431 | doi = 10.3390/biology5040051 | doi-access = free }}</ref>

== Relation to the cell cycle ==
Anaphase accounts for approximately 1% of the [[cell cycle]]'s duration.<ref>{{cite journal | vauthors = Heath IB, Rethoret K | title = Temporal analysis of the nuclear cycle by serial section electron microscopy of the fungus, Saprolegnia ferax | journal = European Journal of Cell Biology | volume = 21 | issue = 2 | pages = 208–13 | date = June 1980 | pmid = 7398661 }}</ref> It begins with the regulated triggering of the metaphase-to-anaphase transition. [[Metaphase]] ends with the destruction of B [[cyclin]]. B cyclin is marked with [[ubiquitin]] which flags it for destruction by [[proteasomes]], which is required for the function of metaphase cyclin-dependent kinases (M-Cdks). In essence, Activation of the [[Anaphase-promoting complex]] (APC) causes the APC to cleave the M-phase cyclin and the inhibitory protein [[securin]] which activates the separase protease to cleave the [[cohesin]] subunits holding the [[chromatids]] together.

== See also ==
* [[Interphase]]
* [[Prophase]]
* [[Prometaphase]]
* [[Metaphase]]
* [[Telophase]]
* [[Cytoskeleton]]
* [[Meiosis#Anaphase I|Anaphase I]]
* [[Meiosis#Meiosis II|Anaphase II]]
* [[Cdc20]]

== References ==
{{reflist}}

== External links ==
* {{commons category inline}}

{{Cell cycle}}

[[Category:Mitosis]]

[[de:Mitose#Anaphase]]