Editing Spindle checkpoint (section)

{{short description|Cell cycle checkpoint}}
[[File:Cell Cycle 2-2.svg|thumb|Steps of the cell cycle. The spindle checkpoint occurs during the M phase.]]
[[File:Spindle chromosomes-en.png|thumb|Scheme showing cell cycle progression between prometaphase and anaphase.]]

The '''spindle checkpoint''', also known as the '''metaphase-to-anaphase transition''', the '''spindle assembly checkpoint''' ('''SAC'''), the '''metaphase checkpoint''', or the '''mitotic checkpoint''', is a [[cell cycle checkpoint]] during [[metaphase]] of [[mitosis]] or [[meiosis]] that prevents the separation of the duplicated [[chromosome]]s ([[Mitosis#Anaphase|anaphase]]) until each chromosome is properly attached to the [[Spindle apparatus|spindle]]. To achieve proper segregation, the two [[kinetochore]]s on the sister [[chromatid]]s must be attached to opposite spindle poles (bipolar orientation).<ref>{{cite journal | vauthors = Santaguida S, Musacchio A | title = The life and miracles of kinetochores | journal = The EMBO Journal | volume = 28 | issue = 17 | pages = 2511–31 | date = September 2009 | pmid = 19629042 | pmc = 2722247 | doi = 10.1038/emboj.2009.173 }}</ref> Only this pattern of attachment will ensure that each daughter [[cell (biology)|cell]] receives one copy of the chromosome. The defining biochemical feature of this checkpoint is the stimulation of the [[anaphase-promoting complex]] by [[mitosis|M-phase]] [[Cyclin-dependent kinase complex|cyclin-CDK complexes]], which in turn causes the [[proteolysis|proteolytic]] destruction of [[cyclin]]s and proteins that hold the [[sister chromatids]] together.<ref>{{Cite book|last=Morgan, David Owen, 1958-|title=The cell cycle : principles of control|date=2007|publisher=New Science Press|isbn=978-0-19-920610-0|location=London|oclc=70173205}}</ref>