Bi1_2011_PS3 - Bi1: The Biology and Biophysics of Viruses...

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Bi1: The Biology and Biophysics of Viruses Spring 2011 Problem Set 3: Central Dogma Due Tuesday, April 19 at 4:00 P.M. in the Bi 1 closet Name: ___________________________________________________________ Section # : _________________________________________________________ Mail Code : ________________________________________________________ TA Names : ________________________________________________________ Date and Time turned in : ____________________________________________ Number of pages including this one : ___________________________________ AFTER YOU FINISH: How long did it take you to complete this problem set? __________________________ Go to the Bi1 moodle site at and take the homework survey There are 2 questions. The number of parts to each question is listed at the beginning of each; be sure to answer all the parts! Grade: Problem 1 __________ Problem 2 __________ TOTAL: _________ HOMEWORK INSTRUCTIONS 1) Turn in your homework stapled to this cover page. 2) Use separate sheets of paper for your answers. 3) Write or type your answers neatly. 4) Put your name on each page of your answers. 5) Box your answers, please, so that the grader can find them. Points may be deducted if you don’t follow these instructions!
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Page 2 of 9 Problem 1: DNA replication (30 points – 4 parts) Readings: Freeman’s ―Biological Science‖ (p. 299-310) You are doing a Caltech SURF exploring possible mechanisms of DNA replication. It’s known that the two strands of double-stranded DNA are antiparallel , where one strand runs in the 5’ 3’ direction and its complement runs in the 3’ 5’ direction. However, there has only been evidence for 5’ 3’ DNA synthesis by DNA polymerase. A DNA polymerase that performs 3’ 5’ synthesis has yet to be discovered. A. (5 points) It may be surprising that, while DNA has strands arranged in both the 5’ 3’ and 3’ 5’ directions, only a 5’ 3’ DNA polymerase has been discovered. Propose two mechanisms to explain this observation. Discuss whether you think each mechanism would be advantageous or disadvantageous and why. Limit your answer to no more than five sentences. (Note that the mechanisms don’t have to be correct – any answer that logically follows from the assumptions you state will receive full credit. For example, you don’t have to assume DNA replication is semi- conservative.) B. Your SURF mentor proposes “semi-discontinuous replication” as a possible mechanism for DNA replication. Semi-discontinuous replication refers to the idea that one strand (known as the leading strand ) is synthesized continuously in the direction that the DNA is being unzipped (thus, this new strand grows towards the replication fork as it opens). The complementary strand (the lagging strand ) is synthesized in discontinuous fragments opposite to the direction that DNA is being unzipped (in this case, each fragment grows away from the opening of the replication
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Bi1_2011_PS3 - Bi1: The Biology and Biophysics of Viruses...

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