Cellular Biology

Stages of Mitosis Explained



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Mitosis, the process where cell division takes place is a very complicated and important process. Mitosis, which takes place in the cell nucleus, consists of many steps; these steps in turn, have several parts to them. The main steps in mitosis are: interphase, prophase, metaphase, anaphase, telophase and cytokinesis. Cytokinesis, while not an official phase of mitosis, is the division of the cell cytoplasm at the end of the mitotic process once daughter cells are formed.

The first phase in mitosis, called interphase can be split up into G (growth) and S (synthesis) phases. In the first G phase aptly named G1, the cell increases in size as it prepares for cell division. After this is the first S phase, DNA is actually synthesized. Once this happens, the cell undergoes the G2 phase where there is more cell growth and proteins are produced. All of this preparation in interphase takes place before prophase starts.

A lot of things happen in the next phase of mitosis called prophase. The chromatin (DNA, RNA and proteins combined together) merge into chromosomes which are held together by a centromere. Spindle fibers as well as microtubles are then formed in the cytoplasm and the cells centrioles (organelles) eventually migrate to opposite sides of the cell. As prophase continues, the cell nucleus membrane disintegrates and the chromosomes move towards the center of the cell.

The next phase in cell division is metaphase. During metaphase the chromosomes line up at the center of the cell along a metaphase plate. This plate is exactly in the middle of the cell where it is equidistant from each spindle pole (formed from the microtubules). The chromosomes line up at the metaphase plate randomly until they eventually attach to either other.

The next phase is anaphase, where the attached chromosomes break apart and move to the opposite ends of the cell. Once there, the “daughter” chromosomes split apart forming single chromatids again.  During this process, the “daughter” chromosomes use the spindle fibers to move to the poles at the opposite ends of the cells.

In telophase, the chromosomes then become sectioned off into new nuclei and daughter cells. These nuclei develop nuclear envelopes and mitosis is basically complete with two new daughter cells formed with genetic information passed on from the parent cell.

The final step, cytokinesis, although not technically a part of mitosis actually takes place near the end of telophase where the two daughter cells now formed split apart into individual cells.

While all of these phases are important, the process of interphase, the cells preparation for cell division takes up to 90 % of the time the cell is undergoing mitosis.

Source:

http://biology.about.com/od/mitosis/ss/mitosisstep.htm

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