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Prob set 2 key - Problem Set 2 Key General Comments on...

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Problem Set 2 Key General Comments on Problem Set 2 and for future problem sets: It is better to draw the gel or other pictures rather than to cut and paste them from somewhere else. I know the cut and paste ones look a lot better which is what your goal was, but I think you learn more from trying to draw it yourself. Chapter 10 problems: Questions: 1. DNA is in the form of a double helix and is thus coiled. Supercoiling is coiling of an already coiled structure. a) What is the difference between positive and negative supercoiling? b) which bacterial enzyme increases negative supercoiling and which can relax negative supercoils? c) what is the general mechanism of action of those enzymes? d) how do the quinolone type of antibiotics affect bacteria? a) positive supercoiling is coiling in a right-handed direction (in the same direction as the double helix (overwinding), negative supercoiling is coiling in a left-handed direction (underwinding). b) topisomerase II (DNA gyrase) increases negative superoiling, while topisomerase I relaxes negative supercoils. c) these enzymes cut the DNA ( a double- stranded break), swivel it and reattach it. 2. a) Please define denaturation and renaturation in your own words. b) Will there be a difference in the temperature at which denaturation occurs for the following two sequences? Please explain. c) Will there be a difference in the rate of renaturation rate? Please explain. d) suppose that sequence 1 is present in many, many copies, while sequence 2 is present in only a few copies in an organisms genome. Will denaturation rate be affected by the difference in copy number? Will renaturation rate be affect by the difference in copy number? 1) AAGATCAATTCTTA 2) GCATACGACGAG TTCTAGTTAAGAAT CGTATGCTGCTC a) denaturation of DNA occurs when heat is applied and the hydrogen bonds break between bases in the two strands.
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