Kinetochore
998893
203400592
2008-04-04T23:03:18Z
Nbauman
2419261
Simplified for introduction to make it readable by ordinary reader.
[[Image:Kinetochore.jpg|frame|right|Image of a human cell showing microtubules in green, chromosomes (DNA) in blue, and kinetochores in pink]]
The '''kinetochore''' (pronounced: kin et' o core) is the protein structure on [[chromosomes]] where the [[spindle fibers]] attach during division to pull the chromosomes apart.
The kinetochore forms in [[eukaryotes]] and assembles on the [[centromere]] and links the [[chromosome]] to microtubule polymers from the [[mitotic spindle]] during [[mitosis]] and [[meiosis]]. The kinetochore contains two regions: an inner kinetochore, which is tightly associated with the [[centromere]] DNA; and an outer kinetochore, which interacts with [[microtubule]]s. "Monocentric" organisms, including vertebrates, fungi, and most plants, have a single centromeric region on each chromosome which assembles one kinetochore. "Holocentric" organisms, including nematodes such as the round worm, assemble a kinetochore along the entire length of a chromosome. During mitosis, which occurs after chromosomes are duplicated
during S phase, two identical "sister" chromatids are held together each with its own kinetochore which face in opposing directions and attach to opposite poles of the mitotic spindle. Following the transition from [[metaphase]] to [[anaphase]], the sister chromatids separate from each other, and the individual kinetochores on each chromatid drive their movement to the spindle poles that will define the two new daughter cells. Thus, the kinetochore is essential for the chromosome segregation that is classically associated with mitosis and meiosis.
Even the simplest kinetochores consist of more than 45 different proteins. Many of these proteins are conserved throughout eukaryote species, including a specialized histone H3 variant (called CENP-A or CenH3) which helps the kinetochore associate with DNA. Other proteins in the kinetochore attach it to the [[microtubule]]s of the [[mitotic spindle]]. There are also [[motor proteins]], including both [[dynein]] and [[kinesin]], which generate forces that move [[chromosome]]s during [[mitosis]]. Other proteins monitor the microtubule attachment as well as the tension between sister kinetochores and activate the [[spindle checkpoint]] to arrest the cell cycle when either of these is absent.
==External links==
* {{MeshNumber|A11.284.170.279.190.160.165.500|Kinetochores}}
[[Category:Organelles]]
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[[zh:着絲粒]]