Anaphase
Anaphase(fromAncient Greekἀνα-(ana-)'back, backward', andφάσις(phásis)'appearance') is the stage ofmitosisafter the process ofmetaphase,when replicatedchromosomesare split and the newly-copied chromosomes (daughterchromatids) are moved to opposite poles of the cell.Chromosomesalso reach their overall maximum condensation in late anaphase, to helpchromosomesegregation and the re-formation of the nucleus.[1]
Anaphase starts when theanaphase promoting complexmarks aninhibitory chaperonecalledsecurinfor destruction byubiquitylatingit. Securin is a protein which inhibits aproteaseknown asseparase.The destruction of securin unleashes separase which then breaks downcohesin,a protein responsible for holding sister chromatids together.[2]
At this point, three subclasses ofmicrotubuleunique to mitosis are involved in creating the forces necessary to separate the chromatids: kinetochore microtubules, interpolar microtubules, andastralmicrotubules.
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.[3]
Once anaphase is complete, the cell moves intotelophase.[4]
Phases
[edit]Anaphase is characterized by two distinct motions. The first of these, anaphase A, moves chromosomes to either pole of a dividing cell (marked bycentrosomes,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
[edit]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 (thecentromere) via protein complexes (kinetochores). 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.[5]
Anaphase B
[edit]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 asdyneinsorkinesins.[6]
Relation to the cell cycle
[edit]Anaphase accounts for approximately 1% of thecell cycle's duration.[7]It begins with the regulated triggering of the metaphase-to-anaphase transition.Metaphaseends with the destruction of Bcyclin.B cyclin is marked withubiquitinwhich flags it for destruction byproteasomes,which is required for the function of metaphase cyclin-dependent kinases (M-Cdks). In essence, Activation of theAnaphase-promoting complex(APC) causes the APC to cleave the M-phase cyclin and the inhibitory proteinsecurinwhich activates the separase protease to cleave thecohesinsubunits holding thechromatidstogether.
See also
[edit]References
[edit]- ^"Chromosome condensation through mitosis".Science Daily.Retrieved12 June2007.
- ^"The Cell Cycle".Kimball's Biology Pages. Archived fromthe originalon 2012-11-19.Retrieved9 December2012.
- ^Hickson GR, Echard A, O'Farrell PH (February 2006)."Rho-kinase controls cell shape changes during cytokinesis".Current Biology.16(4): 359–70.doi:10.1016/j.cub.2005.12.043.PMC1525334.PMID16488869.
- ^Schafer KA (November 1998). "The cell cycle: a review".Veterinary Pathology.35(6): 461–78.doi:10.1177/030098589803500601.PMID9823588.S2CID43902779.
- ^Asbury CL (February 2017)."Anaphase A: Disassembling Microtubules Move Chromosomes toward Spindle Poles".Biology.6(1): 15.doi:10.3390/biology6010015.PMC5372008.PMID28218660.
- ^Scholey JM, Civelekoglu-Scholey G, Brust-Mascher I (December 2016)."Anaphase B".Biology.5(4): 51.doi:10.3390/biology5040051.PMC5192431.PMID27941648.
- ^Heath IB, Rethoret K (June 1980). "Temporal analysis of the nuclear cycle by serial section electron microscopy of the fungus, Saprolegnia ferax".European Journal of Cell Biology.21(2): 208–13.PMID7398661.
External links
[edit]
Media related toAnaphaseat Wikimedia Commons
