NAME STUDENT ID Questions on Prof Urnov s section Question 4 25 points genetics of inducible gene control A E coli and S cerevisiae activate transcription of lacZ and GAL1 10 respectively when lactose and galactose respectively are added to the medium Explain the biological rationale behind this evolutionary conservation 5 points B In a further analogy the addition of glucose to the medium represses transcription both of lacZ and GAL1 10 even if lactose or galactose are also present What is the biological rationale behind this fact 5 points C The rendition of the PaJaMo experiment in your textbook shown on the right is woefully incomplete Write out or draw out the missing part of this experiment the part that convinced Pardee and Jacob Monod that the inducer theory was wrong 10 points D The PaJaMo experiment worked because of two separate features of E coli biology The first is that E coli mate The second 5 points Page 1 of 5 NAME STUDENT ID Question 5 30 points Epigenetic silencing such as X chromosome inactivation is used in many different organisms and for different reasons In class we discussed work from Jasper Rine and Michael Grunstein that led to our present understanding of molecular mechanisms of budding yeast mating type loci silencing In addition to HML and HMR yeast epigenetically silence regions adjacent to their telomeres see schematic below silent telomere active active centromere silent telomere A The RED1 gene makes a product that turns yeast colonies a vivid bright red normal yeast colonies are cream colored Using the drawing above as a template sketch out a chromosome you would engineer to do a screen with RED1 as the reporter gene for genes required for telomeric silencing in yeast 5 points B Explain how you would do the screen using the strain you have just engineered Use a numbered list format for your answer 8 points C Assuming complete conservation of molecular pathways between mating type loci and telomeres in the screen that you are doing what would be the phenotype of a colony that lacks the histone H4 tail A colony lacking the SIR2 gene A colony carrying 2 extra copies of SIR3 and SIR4 9 points H4 SIR2 2 SIR3 SIR4 D In your screen you isolate a mutation that is not linked to any of the histone or SIR loci In this mutant strain the silencing is much stronger than normal Write out the experiment could you do to find out whether the product of this new gene say DOA1 functions upstream or downstream of SIR2 at the telomere 8 points Page 2 of 5 NAME STUDENT ID Question 6 40 points genetics of cancer A As discovered by Harold Varmus and J Michael Bishop retroviruses that cause cancer frequently carry mutated version of normal cellular genes called protooncogenes An interesting feature of such stolen protooncogenes is they do not belong to the same functional category src is a receptor tyrosine kinase ras is a G protein myc is a transcription factor How can different viruses accomplish the same goal oncogenic transformation of the cell by using completely different proteins 10 points B A mouse knockout for p53 has a remarkable phenotype the animal goes through embryonic development and its childhood with no seeming abnormalities but by 6 months of age succumbs to multiple tumors and dies Explain the reason for the delayed onset of cancer in this animal 10 points C Humans who carry germline mutations in pRB are predisposed to cancer of the retina This is just one of many known examples of inherited cancer in humans A common and interesting aspect of many hereditary cancer syndromes is they exhibit a dominant mode of inheritance What three different types of mutation could act in such a dominant fashion For full credit illustrate your answer with examples of cellular genes affected by such mutations in cancer clearly explaining why these mutations are dominant 12 points 1 2 3 D Gleevec is highly efficient in the treatment of chronic myelogenous leukemia Most significantly over 80 of CML patients respond to Gleevec even when it is used in a singleagent regimen i e by itself This is puzzling because Gleevec inhibits the activity of the oncogene bcr abl but the cancer cell still has mutations both in p53 and pRB and Gleevec has does not affect either one of those How can Gleevec be effective if it doesn t address all the mutations in the cancer cell 8 points Page 3 of 5 NAME STUDENT ID Question 7 40 points A Leland Hartwell received a Nobel prize for his studies on cell cycle control in budding yeast S cerevisiae His forward genetic screen identified a large number of cdc genes in the yeast genome products of which are required for the cell to correctly execute the G1 S G2 M sequence Given that inability to divide leads to cell death a phenotype that can be invoked by mutating many different genes Hartwell used an elegant trick to ensure that the mutants he identified were specifically in the cell cycle control machinery as opposed to some other essential cell system e g glycolysis or RNA polymerase What was that trick 10 points B The most important gene identified by Hartwell CDC28 codes for a cyclin dependent kinase that is required for yeast to traverse the start point of the cell cycle Cdc28p functions in a complex with a cyclin a protein that directs the kinase to act on specific substrates the interaction with the cyclin is absolutely required for Cdc28p function in driving the cell cycle Describe in reasonable detail a set of genetic experiments that would prove or at least strongly suggest that Cdc28p physically interacts with Cln1p the product of the CLN1 gene a major cyclin in yeast Please format your answer as a numbered list at each step describe the strains data conclusions that lead you to the next step Hint you do not have to be particularly inventive here since we extensively discussed such an experimental set in the context of a different biological system your challenge is to think carefully about how to port those experiments to this particular situation 30 points Page 4 of 5 NAME STUDENT ID Page 5 of 5
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