Final Exam QA Bio115 Spring 2007

Final Exam QA Bio115 Spring 2007 - Bio115 Spring 2007 Final...

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Bio115 Spring 2007 Final Exam Q1 (2+8 points) The expression of genetic information requires two template-based polymerisation reactions. a. Name the two polymerization reactions. b. What are the templates, products and catalyzing enzymes of both reactions, and which type of bond is formed in either reaction? A1 a. Transcription and translation. b. Transcription: The template is DNA, the product RNA, bonds formed are phosphoester bonds. The catalyzing enzyme is RNA polymerase. Translation: The template is mRNA, the product is a polypeptide, bonds formed are peptide bonds. The catalyzing enzyme is the ribosome. Q2 (6 points) a. Draw the chemical structure of 5’ monophosphate deoxyadenosine. b. Indicate and name the adenine atom that becomes accessible to methylation by dimethylsulfate upon melting of DNA, and explain the reason for the accessibility difference. A2 b. Atom N1. In double stranded DNA the lonesome electron pair of N1 is engaged in a hydrogen bond with thymine. Q3 (2+4 points) a. Assume, a method is available to you that allows you to measure the frequency with which any of the 16 possible dinucleotides 5’-XY-3’ (X, Y= A, C, G, T) occurs in both strands of a DNA molecule. How can this information be used to determine whether the two strands run parallel or antiparallel? Base your argument, for example, on the dinucleotide 5’-GA-3’ that occurs with frequency f in one of the two strands. (Hint: Which dinucleotide occurs with frequency f in the complementary strand?) b. Which experimental observation indicated to Watson and Crick that the two strands of the DNA double helix have antiparallel orientation? A3 a. If the strands run parallel, 5’-CT-3’ occurs with frequency f in the complementary strand. If the strands run antiparallel, 5’-TC-3’ occurs with frequency f in the complementary strand. b. X-ray crystallography indicated that the sugar-phosphate backbone of DNA has dyad symmetry about the axis perpendicular to the long axis of the DNA. This ruled out the possibility that the two stands have the same orientation. Q4 (3+1+1+1 points) a. At which position are tRNAs aminoacylated? b. What is the name of the chemical bond that links amino acids to their tRNAs? c. What is the name of the chemical bond that links two amino acids in a polypeptide?
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d. Which of the two bonds in b. and c. is thermodynamically more stable. A4 a. The 2’ or 3’ hydroxyl group of the 3’-terminal nucleotide. b. Ester bond. c. Peptide bond. d. The peptide bond. Q5 (6 points) Which are the chemical reactions catalyzed by aminoacyl-tRNA synthetases? A5 a. Adenylylation of tRNA (amino acid activation). b. Ester bond formation between amino acid and tRNA. c. Cleavage of amino acid from either AMP or the tRNA (proofreading).
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Final Exam QA Bio115 Spring 2007 - Bio115 Spring 2007 Final...

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