exam_3S

exam_3S - Solutions to 7.012 Quiz III Class Ave = 70.5...

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Unformatted text preview: Solutions to 7.012 Quiz III Class Ave = 70.5 Standard Dev = 12.5 Approximate grade Range % A 83 - 100 19% B 70 - 82 37% C 56 - 69 30% D 45 55 12% F 0 43 2% Initials_____________ 2 Question 1 (14 points) You discover several new viruses. a) Virus A is a positive-stranded (mRNA-like) RNA virus, but is not a retrovirus. The viral genome is enclosed by nucleocapsid proteins and enveloped by a membrane that contains surface viral glycoproteins. Would this virus need to package within the viral particle any additional protein or proteins to successfully reproduce within a host cell? If the answer is yes, state why additional protein(s) must be packaged and what protein(s) must be packaged. If the answer is no, explain why no additional protein needs to be packaged. No. Although this virus must encode an RNA-directed RNA polymerase, it does not have to package it, because the genome can be directly translated into the needed protein. Name the type of enzyme that this virus would use to copy its genome. Is this enzyme encoded by the virus or the host? RNA-directed RNA polymerase encoded by the virus. b) Virus B is a negative-stranded RNA virus and it does not integrate into the host genome. The viral genome is enclosed by nucleocapsid proteins, which form an icosahedral capsid. Would this virus need to package within the viral particle any additional protein or proteins to successfully reproduce within a host cell? If the answer is yes, state why additional protein(s) must be packaged and what protein(s) must be packaged. If the answer is no, explain why no additional protein needs to be packaged. Yes. This virus must encode an RNA-directed RNA polymerase, and because the genome is can not be translated within the host cell, it must package this enzyme. c) Virus C is a small double-stranded DNA virus and it does not integrate into the host genome. The viral genome is enclosed by nucleocapsid proteins, and no additional proteins are packaged within the viral particle. To maintain a small genome, this virus encodes only proteins that are absolutely required. Name the type of enzyme that this virus would use to copy its genome. Is this enzyme encoded by the virus or the host? DNA directed DNA polymerase from the host cell. You know that some viruses, like the influenza viruses change over relatively short periods of time. You examine the genomes of the new virus particles for viruses A, B, and C, and find that the mutation rate for one of the viruses is much less than that for the other two viruses. Which virus do you expect will have the lowest mutation rate? Explain why you made this choice. Virus C uses the host DNA polymerase which has proofreading capabilities and thus will make fewer Initials_____________ 2 Question 1 (14 points) You discover several new viruses....
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This note was uploaded on 03/12/2011 for the course BIO 7.012 taught by Professor Lander during the Fall '10 term at MIT.

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exam_3S - Solutions to 7.012 Quiz III Class Ave = 70.5...

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