8. Progression through the cell cycle is tightly regulated. In particular, we looked at how the cell regulates entry into S phase. A. Please illustrate the steps involved in a cell’s decision to enter S phase. Include the relevant proteins, including the proteins involved in the DNA damage checkpoint that we discussed. You may use a diagram if you wish (6 points). B. Cells have checkpoints at several points during the cell cycle that they can implement if needed. Briefly explain the purpose of these checkpoints (4 points). The purpose of checkpoints is for the cell to verify that it is safe to move on through the cell cycle and that there are no significant problems. For example, one verifies that there is no DNA damage before replicating the DNA. Another confirms that chromosomes are properly attached to the spindle before moving through mitosis. C. Using the pathway discussed in lecture, first determine whether the following mutations would increase or decrease the probability of cancer, or have no effect. Please briefly state your rationale (8 points). Mutation Probability Rationale decrease Loss of cyclin Constitutively active increase Ras (i.e. always active) Mutation that leads increase to Bcl2 overproduction Non-phosphorylatable but otherwise decrease Functional Rb plus loss of p53
8. Progression through the cell cycle is tightly regulated. In particular, we looked at how the cell regulates entry into S phase. A. Please illustrate the steps involved in a cell’s decision to enter S phase. Include the relevant proteins, including the proteins involved in the DNA damage checkpoint that we discussed. You may use a diagram if you wish (6 points). B. Cells have checkpoints at several points during the cell cycle that they can implement if needed. Briefly explain the purpose of these checkpoints (4 points). The purpose of checkpoints is for the cell to verify that it is safe to move on through the cell cycle and that there are no significant problems. For example, one verifies that there is no DNA damage before replicating the DNA. Another confirms that chromosomes are properly attached to the spindle before moving through mitosis. C. Using the pathway discussed in lecture, first determine whether the following mutations would increase or decrease the probability of cancer, or have no effect. Please briefly state your rationale (8 points). Mutation Probability Rationale Loss of cyclin decrease Constitutively active increase Ras (i.e. always active) Mutation that leads increase to Bcl2 overproduction Non-phosphorylatable but otherwise decrease Functional Rb plus loss of p53