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MIT 7 012 - Problem Set #5

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Name: _____________________________ 1 2006 7.012 Problem Set 5 ** Due before 5 PM on THURSDAY, November 9, 2006. ** Turn answers in to the box outside of 68-120. PLEASE WRITE YOUR ANSWERS ON THIS PRINTOUT. 1. You are studying the development of a new species of frog. A fertilized frog egg of this species (which is diploid) is produced when two haploid gametes (i.e. an egg from the mother frog and a sperm from the father frog) fuse. (a) When these two gametes fuse, which gamete do you think contributes the vast majority of the cytoplasm and organelles? When a fertilized egg begins development, the outcome of the first three cell cycles look like this: Cell cycle #1 Cell cycle #2 Cell cycle #3 (b) Cell growth normally occurs in G1 stage and/or G2 stage of the cell cycle. Based on the above picture, do you think that the cell cycles occurring during this early phase of development involve a large amount of cell growth? You examine the localization of a specific protein during each of these four early developmental stages. This protein is required for the formation of ectoderm. The location of the protein is indicated by gray shading. (c) At the four cell stage, do you think that the four cells are equivalent in terms of the different fates their daughter cells can take on?Name: _____________________________ 2 You examine the localization of a specific mRNA during each of these four early developmental stages. The location of the mRNA is indicated by gray shading. (d) Given that these frog embryos do not begin their own transcription until part of the way through the blastula stage, when do you think this mRNA was produced and by whom? You examine the localization of a different specific protein during each of these four early developmental stages. The location of the protein is indicated by gray shading. (e) Draw two different patterns for what you might see if you examined the sub-cellular localization pattern of the mRNA that encodes this protein in the single-celled fertilized egg. One of the two possibilities should imply that this gene is regulated at the level of translation. Draw the two potential patterns of mRNA localization as shading in the two eggs provided for you below. In this picture at the 8-cell stage, the cell marked with a star gives rise to only ectoderm. *Name: _____________________________ 3 (f) In one or two sentences, describe what experiment you would do to arrive at this conclusion, and what result you would get from this experiment that would allow you to make this conclusion. 2. You are a developmental biologist studying pattern formation in fruit flies. In your efforts to understand how body patterns of gene expression in flies are regulated, you have recently identified a DNA-binding protein, B, which is present in a gradient in the embryo, as drawn below. B binds to the promoter of the X gene and helps RNA polymerase bind there. X protein, when produced, binds to the promoter of Z and impedes the binding of RNA polymerase there. (a) Into which specific category of proteins does protein B fall, given its function? (b) Into which specific category of proteins does protein X fall, given its function? [B] 3 (arbitrary units) length posterior anterior 1 0 2Name: _____________________________ 4 (c) At what level of gene regulation is the X gene regulated? Your choices are: transcriptional, post-transcriptional, translational, or post-translational. (d) Using the format used above, draw a line in the graph to indicate what you think the levels of Z look like across the embryo: Proteins X and Z both bind to the promoter region of gene Y, and both proteins impede RNA polymerase from binding there. Both X and Z must be bound to the Y promoter to impede RNA polymerase from binding. (e) Using the format used above, draw a line in the graph to indicate what you think the levels of Y look like across the embryo: [Z] 3 (arbitrary units) length posterior anterior 1 0 2 [Y] 3 (arbitrary units) length posterior anterior 1 0 2Name: _____________________________ 5 You make a strain of fruit fly by genetic engineering that lacks the promoter region in front of the X gene on both homologs. Draw the patterns of Z and Y expression you would expect in this mutant embryo in the graphs below. (f) Using the format used above, draw a line in the graph to indicate what you think the levels of Z look like across this mutant embryo: (g) Using the format used above, draw a line in the graph to indicate what you think the levels of Y look like across this mutant embryo: [Z] 3 (arbitrary units) length posterior anterior 1 0 2 [Y] 3 (arbitrary units) length posterior anterior 1 0 2Name: _____________________________ 6 You make a strain of fruit fly by genetic engineering that is expressing B protein at equal levels (at 3 “arbitrary units”) evenly across the entire embryo. Draw the patterns of Z and Y expression you would expect in this mutant embryo in the graphs below. (h) Using the format used above, draw a line in the graph to indicate what you think the levels of Z look like across this mutant embryo: (i) Using the format used above, draw a line in the graph to indicate what you think the levels of Y look like across this mutant embryo: [Z] 3 (arbitrary units) length posterior anterior 1 0 2 [Y] 3 (arbitrary units) length posterior anterior 1 0 2Name: _____________________________ 7 3. The eye cancer retinoblastoma is usually caused by mutations in the Rb gene. The wild-type function of Rb is to keep proteins that promote the cell cycle inactive unless the cell is supposed to be growing and dividing. Rb does this by binding and inhibiting


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MIT 7 012 - Problem Set #5

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