Kinetochore

A kinetochore (kᵻˈnɛtəkɔər, -ˈniːtəkɔər) is a disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart. The kinetochore assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis. The term kinetochore was first used in a footnote in a 1934 Cytology book by Lester W. Sharp and commonly accepted in 1936. Sharp's footnote reads: "The convenient term kinetochore (= movement place) has been suggested to the author by J. A. Moore", likely referring to John Alexander Moore who had joined Columbia University as a freshman in 1932. Monocentric organisms, including vertebrates, fungi, and most plants, have a single centromeric region on each chromosome which assembles a single, localized kinetochore. Holocentric organisms, such as nematodes and some plants, assemble a kinetochore along the entire length of a chromosome. Kinetochores start, control, and supervise the striking movements of chromosomes during cell division. During mitosis, which occurs after the amount of DNA is doubled in each chromosome (while maintaining the same number of chromosomes) in S phase, two sister chromatids are held together by a centromere. Each chromatid has its own kinetochore, which face in opposite directions and attach to opposite poles of the mitotic spindle apparatus. 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. The kinetochore is therefore essential for the chromosome segregation that is classically associated with mitosis and meiosis. The kinetochore contains two regions: an inner kinetochore, which is tightly associated with the centromere DNA and assembled in a specialized form of chromatin that persists throughout the cell cycle; an outer kinetochore, which interacts with microtubules; the outer kinetochore is a very dynamic structure with many identical components, which are assembled and functional only during cell division.