121MT2IvoryKey

121MT2IvoryKey - Name Last, Key, Ivory First MCB121, Page 1...

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Name Key, Ivory MCB121, Page 1 of 8 Last, First Burgess, Gasser Student Authorization: I, , authorize the University to distribute publicly this graded exam ( e. g. , handed out in class, or left in a bin for me to pick up). Signature Date MCB121-01, Winter, 2008 Second Midterm, March 4, 2008 Instructions: There are eight pages in this exam including the cover sheet, please count them before you start to make sure all are present. Write your name on each page of the exam. Write your answers in the space provided below each question. If you need more space use the back of the page and indicate clearly that you have continued your answer on the back. Do not use additional paper. Amino acid Abbreviations Amino acid Abbreviations Alanine Ala A Leucine Leu L Arginine Arg R Lysine Lys K Asparagine Asn N Methionine Met M Aspartic acid Asp D Phenylalanine Phe F Cysteine Cys C Proline Pro P Glutamine Gln Q Serine Ser S Glutamic Acid Glu E Threonine Thr T Glycine Gly G Tryptophan Trp W Histidine His H Tyrosine Tyr Y Isoleucine Ile I Valine Val V Question Value Score 1 15 2 22 3 16 4 20 5 15 6 19 7 6 8 10 9 12 10 15 Total 150
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Name Key, Ivory MCB121, Page 2 of 8 Last, First Burgess, Gasser 1. (15) You have been gazing at the nucleotide sequences of the U2 and U6 snRNAs and notice a region of complementary sequences between the two which has not been described to date. You wonder if this potential base pairing interaction might play a role in the process of mRNA splicing. To address this problem, you make a C to G mutation in U2 (called U2CG) and a G to C mutation in U6 (called U6GC) at nucleotides that would presumably destabilize the putative base pair interaction. The two mutations combined (U2CG/U6GC ) would restore base pairing interaction. You make nuclear extracts containing mutated forms of U2 and/or U6 and add radiolabeled pre- mRNA and ATP. After 20 minutes incubation you isolate RNA and run these samples on a poly- acrylamide gel. As a control you include a reaction using extract with nonmutated forms of the snRNAs (U2/U6). Below is an autoradiogram of what you see. a) Indicate the products and/or intermediates of the splicing reaction using a diagram to the left of the gel. The pre-mRNA substrate is given. See above. b) Which step of splicing appears to be affected by U2CG and the U6GC mutations? Second step: The mutations have allowed for the first step of splicing since the lariat intermediate and unligated exon 1 are present. Since no spliced product or lariat intron product is seen we can conclude that the mutations affect the 2 nd step of splicing c) From these results do you think your hypothesis is correct? Explain briefly.
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121MT2IvoryKey - Name Last, Key, Ivory First MCB121, Page 1...

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