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It is referred to as the mitotic spindle during mitosis, a process that produces genetically identical daughter cells, or the meiotic spindle during meiosis, a process that produces gametes with half the number of chromosomes of the parent cell. Besides chromosomes, the spindle apparatus is composed of hundreds of proteins.
The spindle checkpoint, or SAC (for spindle assembly checkpoint), also known as the mitotic checkpoint, is a cellular mechanism responsible for detection of: correct assembly of the mitotic spindle; attachment of all chromosomes to the mitotic spindle in a bipolar manner; congression of all chromosomes at the metaphase plate.
Astral microtubules anchor the spindle poles to the cell membrane. Microtubule polymerization is nucleated at the microtubule organizing center . An aster is a cellular structure shaped like a star , consisting of a centrosome and its associated microtubules during the early stages of mitosis in an animal cell.
Animal cell cytokinesis starts with the stabilization of microtubules and reorganization of the mitotic spindle to form the central spindle. The central spindle (or spindle midzone ) forms when non-kinetochore microtubule fibers are bundled between the spindle poles.
Mitosis consists of two independent processes: the intra-chromosomal and the extra-chromosomal (formation of spindle) changes both of these being in total coordination of each other. This cell as seen under immunofluorescence contains four centrosomes, two at each end, with their own spindle fibers attaching to chromosomes at the metaphase plate.
After the chromosomes line up in the middle of the cell, the spindle fibers will pull them apart. The chromosomes are split apart while the sister chromatids move to opposite sides of the cell. [29] As the sister chromatids are being pulled apart, the cell and plasma are elongated by non-kinetochore microtubules. [30]
An acentric chromosome is fragment of a chromosome that lacks a centromere. Since centromeres are the attachment point for spindle fibers in cell division, acentric fragments are not evenly distributed to daughter cells during cell division. As a result, a daughter cell will lack the acentric fragment and deleterious consequences could occur.
This spindle apparatus consists of microtubules, microfilaments and a complex network of various proteins. During metaphase, the chromosomes line up using the spindle apparatus in the middle of the cell along the equatorial plate. The chromosomes move to opposite poles during anaphase and remain attached to the spindle fibers by their centromeres.