Bi1_2011_PS3_solution

Bi1_2011_PS3_solution - Bi1: The Biology and Biophysics of...

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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: ANSWER KEY ________________________________________________ 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 http://courses.caltech.edu/ 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 12 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.) These answers are just samples! Full credit given for anything that follows logical reasoning! Mechanism: discontinuous replication on one strand -Advantage: don’t have to unzip the DNA all the way (replication is faster) -Disadvantage: need more proteins to be involved Mechanism: both strands are fully unzipped before the 3’ 5’ strand is replicated -Advantage: not as much need for ligase/primase action -Disadvantage: time-consuming/energy costly, need to prevent long strands from rehybridizing Mechanism: replication is not semi-conservative and is dispersive instead – the DNA
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Bi1_2011_PS3_solution - Bi1: The Biology and Biophysics of...

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