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This 1 page Class Notes was uploaded by zjidah on Sunday May 8, 2016. The Class Notes belongs to CDS 151LEC at Kent State University taught by Staff in Spring 2016. Since its upload, it has received 10 views.
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Date Created: 05/08/16
CHAPTER 4 THE STRUCTURE OF DNA 1. Consider a G:C base pair. a. Which edge of each base pair faces into the major groove and which into the minor groove? b. Which atoms are hydrogen bond donors or hydrogen bond acceptors? c. Why do G:C base pairs contribute more to DNA helix stability than A:T base pairs? 2. Other than hydrogen bonding, what else contributes to the stability of the double helix? 3. The virion DNA of an E. coli phage called ΦX174 has the base composition: 25% A, 33% T, 24% G, and 18% C. What do these data suggest about the structure of the phage's chromosome? 4. Describe the ways in which DNA can vary from its ideal B structure, and contrast the B form of DNA with the A and Z forms. What factors or conditions favor these deviations from the B form and the choice between the three possible forms? 5. Consider a covalently closed, circular DNA molecule of length 10,500 base pairs and Lk 950. What is the effect of the binding of 110 molecules of ethidium on Lk, Tw, and Wr? Hint: The addition of ethidium does not affect the Lk but the addition of each molecule of ethidium will decrease the local twist of DNA by 26° (from about 10° to about 36°, resulting in one fewer turn of the DNA for every approximately 14 (360°/26°) bound molecules of ethidium. Therefore, if there are 110 bound molecules of ethidium, there will be a decrease of about 8 turns of the DNA (110/14). 6. Describe three differences between topoisomerase I and topoisomerase II. You have an experiment in mind that requires topoisomerase II, but not topoisomerase I, and would like to purify this enzyme from bacterial cells. Describe a purification strategy that would allow you to specifically isolate topoisomerase II, relying on the unique activities of each enzyme. 7. Populations of the following types of molecules are incubated with the indicated enzymes. Predict all possible products for each reaction. a. complementary single-stranded circles + topoisomerase I b. negatively supercoiled DNA + eukaryotic topoisomerase II c. negatively supercoiled DNA + topoisomerase I