Exam 3 2007 - 1 NAME _ One strand of a section of DNA...

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NAME ________________________________ 1 One strand of a section of DNA isolated from the bacterium E. coli reads: 5 - GTAGCCTACCCATAGG -3 A. Suppose that an mRNA is transcribed from this DNA using the complementary strand as a template. What will be the sequence of the mRNA in this region (make sure you label the 5 and 3 ends of the mRNA)? (2pts) B. How many different peptides could potentially be made from this sequence of RNA, assuming translation initiates upstream of this sequence? (2pts) C. What are these peptides? (Give your answer using the one letter amino acid code.) (2pts) 2 A strain of yeast translates mRNA into protein with a high level of inaccuracy. Individual molecules of a particular protein isolated from this yeast have the following variations in the first 11 amino acids compared with the sequence of the same protein isolated from normal yeast cells (see figure below). What is the most likely cause of this variation in protein sequence? Explain your answer. (Refer to codon table provided above) (3pts) 1
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NAME ________________________________ (a) A mutation in the DNA coding for the protein (b) A mutation in the anticodon of the isoleucine tRNA (tRNA Ile ) (c) A mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different amino acids (d) A mutation in the isoleucyl-tRNA synthetase that decreases its ability to distinguish between different tRNA molecules (e) A mutation in a component of the ribosome that allows binding of incorrect tRNA molecules to the A-site 3 You have discovered a protein that inhibits translation. When you add this inhibitor to a mixture capable of translating human mRNA and centrifuge the mixture to separate polyribosomes and single ribosomes, you obtain the results shown in figure below. Which of the following interpretations are consistent with these observations? (4pts) (a) The protein binds to the small ribosomal subunit and increases the rate of initiation of translation. (b) The protein binds to sequences in the 5 region of the mRNA and inhibits the rate of initiation of translation. (c) The protein binds to the large ribosomal subunit and slows down elongation of the polypeptide chain. (d) The protein binds to sequences in the 3 region of the mRNA and prevents termination of translation. 2
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NAME ________________________________ 4 The concentration of a particular protein X in a normal human cell rises gradually from a low point, immediately after cell division, to a high point, just before cell division, and then drops sharply. The level of its mRNA in the cell remains fairly constant throughout this time. Protein X is required for cell growth and survival, but the drop in its level just before cell division is essential for division to proceed. You have isolated a line of human cells that grow in size in culture but cannot divide, and on analyzing these mutants, you find that levels of X mRNA in the mutant cells are normal. Which of the following mutations in the gene for
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Exam 3 2007 - 1 NAME _ One strand of a section of DNA...

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