- Kinetochore
The kinetochore (pronounced: kin et' o core) is the protein structure on
chromosomes where thespindle fibers attach during division to pull the chromosomes apart.The kinetochore forms in
eukaryotes and assembles on thecentromere and links thechromosome to microtubule polymers from themitotic spindle duringmitosis andmeiosis . The kinetochore contains two regions: an inner kinetochore, which is tightly associated with thecentromere DNA; and an outer kinetochore, which interacts withmicrotubule 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 frommetaphase toanaphase , 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 themitotic spindle . There are alsomotor proteins , including bothdynein andkinesin , which generate forces that movechromosome s duringmitosis . Other proteins monitor the microtubule attachment as well as the tension between sister kinetochores and activate thespindle checkpoint to arrest the cell cycle when either of these is absent.External links
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