6 Cell Cycle 2 Study Guide Answers

6 Cell Cycle 2 Study Guide Answers - BS 111 (Kopachik)...

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BS 111 (Kopachik) Answers to Cell Cycle II Regulation 1. Describe the three checkpoints. Give name, location in cell cycle, purpose. The checkpoint in late G 1 called G 1 Checkpoint or Start gets input signals for proper nutrients, growth factors and cell size so the cell can determine if it should start DNA synthesis. Once started DNA synthesis always is completed. Another main checkpoint occurs in the late G 2 to M phase (the G 2 checkpoint) in which the cell assesses whether the DNA is properly replicated and not damaged and should then condense chromosomes and segregate them to the poles of the cells. A third checkpoint occurs at mid-mitosis and is called the M or spindle assembly checkpoint. Here the main determination is made to whether all the chromosomes are attached to the spindle through their kinetochores. More generally the checkpoints are the only times at which a cell will stop in the cell cycle to assess its condition for going on in the cycle. 2. What is the evidence that the eukaryotic cell cycle is controlled by cyclins and cyclin dependent kinase activity? What is MPF? What regulatory proteins fluctuate in amount, in activity during phases of the cell cycle and at what time is this done? What cytoskeletal protein’s amount would also vary in the cell cycle? Evidence for cyclins regulating the cell cycle comes from the fact that their levels go up and down in a predictable way with the cell cycle. For instance cyclin B increases through G 2 to reach a peak in M. The cyclins are not enzymes but rather they activate by binding to the cyclin dependent kinases of which mitosis (maturation) promotion factor (MPF) is the main one for triggering the mitotic events. MPF and other CDKs do not vary in amount but they do vary in activity which is controlled by their associated cyclin. A cytoskeletal protein whose level increases in mitosis is tubulin for the spindle but this protein plays a structural not a regulatory role in the cell cycle. 3.
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6 Cell Cycle 2 Study Guide Answers - BS 111 (Kopachik)...

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