Exam 2007 key - LS4 Final Exam-Fall 2007 Name: University...

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LS4 Final Exam—Fall 2007 Name: University ID: Instructions: There are 10 problems on this exam. Each is worth 15 points. 1. Make your answers clear and concise. 2. Use the back of each sheet to work out the problems. If you need more blank paper, raise your hand and we’ll bring it to you. Try to write only your final answer on the exam question itself. Circling answers helps too. 3. Do not write in the boxes. They are for grading purposes. 4. Be sure to write your name and ID on every page. 1 point will be deducted for each page without your name. Score: Problem 1 Problem 6 Problem 2 Problem 7 Problem 3 Problem 8 Problem 4 Problem 9 Problem 5 Problem 10 Total
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Name and ID: Problem 1 On a recent trip to outer space, astronauts isolated an alien bacterium that has a similar biology to life on earth. You have been asked to determine whether or not it uses the same type of genetic code that is found on earth. One of your first observations is that while the organism uses A, T, C and G as nucleotides, there are two additional nucleotides that pair with one another, R and S. You have also studied the organism’s proteins and have concluded that there are 32 amino acids. A) What is the minimum codon length (number of nucleotides that encode an amino acid) required by these alien bacteria? (3 points) Only 2 nucleotides are needed at minimum, because with 6 possible nucleotides, 36 possible codons (6x6) are possible with just 2 positions. B) You clone a gene from the alien bacteria that is required for survival without oxygen. Starting with a wild-type strain of bacteria (can live without oxygen) you use acridine orange to induce a single base pair insertion into the 5’ end of this gene. The resulting bacteria can still live without oxygen. Based on this result, do you think the bacteria have an overlapping or non-overlapping code? Explain your answer. (4 points) The code must be overlapping. If the code were non-overlapping the insertion of a single base would cause a frameshift mutation and alter the identity of everything downstream of the insertion. Because the insertion occurred at the 5’ end that would mean that the majority of the protein would be mutant if the code were non-overlapping. If the code were overlapping then only a few amino acids would be altered due to the insertion. C) You decide to further study the nature of the code by inserting a single base into the middle portion of the gene. Surprisingly, this results in bacteria that are unable to live without oxygen. Propose an explanation for this result. (4 points) The insertion must have occurred in a region of the gene that is critical for protein function. The few amino acids that were altered by the insertion were critical for normal protein function. Alternatively, you may also have created a stop codon by inserting the nucleotide D) To test your preliminary conclusions you mutate a single S in the gene to an A. You then translate the gene in vitro and sequence the resulting protein. You find that two
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This note was uploaded on 02/15/2012 for the course PMB 13 taught by Professor Freeling during the Spring '09 term at University of California, Berkeley.

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Exam 2007 key - LS4 Final Exam-Fall 2007 Name: University...

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