Mitosis160-page13

Mitosis160-page13 - In addition to the checkpoint controls...

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Cell Reproduction: Mitosis - 13 The G 1 and G 2 checkpoint signals involve a set of enzymes, called cyclin- dependent kinases (Cdks), because they are activated by proteins called cyclins, whose concentration is cyclical (hence cyclin). Cyclin is a cyclin- dependent kinase allosteric regulator molecule. Cyclin concentration rises and falls during the cell cycle in response to growth factor signal molecules. When levels are high, cyclins combine with the cyclin-dependent kinases (Cdks) forming a complex (cyclin-Cdk). When activated by their regulator cyclin, the cyclin-dependent kinases phosphorylate specific proteins needed to do mitosis. The phosphorylated proteins change shape to initiate important steps in the cell cycle.
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Unformatted text preview: In addition to the checkpoint controls of cell division, the cell has a variety of controls that monitor the processes and regulate checkpoint activities. Some of these regulators are critical in cancer formation, and are the subject of much research. For example, Rb is one of the phosphorylated proteins, and functions in the G 1 checkpoint promoting DNA synthesis. P53 is a protein that monitors DNA for damage, and when DNA damage is found, normally blocks the activity of Rb and initiates DNA repair activity. If DNA cannot be repaired, P53 initiates apoptosis, a means of cell death. Both defective Rb and defective P53 genes are associated with cancers....
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