706_S2006_PS4 - 7.06 Problem Set Four, 2006 1. Explain the...

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7.06 Problem Set Four, 2006 1. Explain the molecular mechanism behind each of the following events that occur during the cell cycle, making sure to discuss specific proteins that are involved in making each event happen. (a) During G1 phase, cells pass through the Restriction Point if growth factors are present in the cell medium. (b) During S phase, origins of replication fire. (c) During S phase, each origin of replication never fires more than once. (d) During prophase of mitosis, chromosomes become condensed. (e) During prophase of mitosis (in many cell types, but not in yeast), the nuclear membrane breaks down. (f) During prophase and metaphase of mitosis, the mitotic spindle forms. (g) During prophase and metaphase of mitosis, chromosomes attach to microtubules. (h) During metaphase of mitosis, chromosomes become aligned. (i) At the metaphase-to-anaphase transition of mitosis, sister chromatids become separated. (j) During anaphase of mitosis, sister chromatids are pulled to opposite poles.
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2. Below are listed four different mechanisms of regulating of cyclin/CDK activity. For each mechanism: (i) Explain how that mechanism regulates cyclin/CDK activity. (ii) Describe an experiment you could do to show that cyclin/CDKs are indeed regulated in that way. Be sure to mention the result you would get that would demonstrate that such a type of regulation is indeed occurring. (a) Phosphorylation by Wee1 (b) Dephosphorylation by Cdc25 (c) Binding by the inhibitor p21 (d) Degradation of cyclins by the 26S proteasome 3. The surprise success of this year’s Oscar-winning documentary, March of the Penguins , has spurred a sudden resurgence in penguin research in molecular biology labs across the globe. Of particular concern is the threat posed to penguins from increased exposure to UV radiation, brought about by the expanding hole in the protective ozone layer over Antarctica. As a concerned scientist and avid penguin lover, you decide to study the mechanisms that penguin cells employ to protect themselves from UV-induced DNA damage. Conveniently, Morgan Freeman, while narrating the documentary, cultured some penguin cells and brought them back to your lab where you can grow and study them. However, as much as you appreciate his generous contribution to your scientific endeavors, you decide that it would be much easier to carry out a genetic screen to hunt for mutants that cannot protect themselves from DNA damage in a simpler system, Schizosaccharomyces pombe .
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This note was uploaded on 01/23/2012 for the course BIOLOGY lsm1301 taught by Professor Seow during the Spring '11 term at National University of Singapore.

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706_S2006_PS4 - 7.06 Problem Set Four, 2006 1. Explain the...

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