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LEC03a - Figure 2.10 Melting temperature Temperature at which ½ of DNA molecules are denatured DNA molecules are denatured Beyond the double the

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Unformatted text preview: Figure 2.10 Melting temperature: Temperature at which ½ of DNA molecules are denatured DNA molecules are denatured Beyond the double the double helix Unusual DNA Secondary Structures Supercoiling of DNA can be described by Linking number, Twist and Writhe L=T+W relaxed supercoiled Linking number: the number of times that each strand winds around the other L=4 T=4 When there are no supercoils, L=T When linear DNA is ligated to form closed circular DNA, it can be either relaxed or strained. Conforms to B-DNA not B-DNA A strained circle can then become “supercoiled” to relieve the tension L=T+W =10-1=9 Alternatively, the strained circular DNA can partially unwind or flip into a cruciform structure. Topoisomerases are enzymes that alter the supercoiling of DNA topoisomers Type I Topoisomerases break one strand of the DNA, allow the DNA to unwind and then religate Energy is retained in a new phosphodiester bond between the DNA and protein. Even in linear chromosomes DNA can form DNA can form loops that can be either relaxed or supercoiled Two types of topoisomerases Type I: relax supercoiled DNA ! Type I: relax supercoiled DNA without need for ATP ! Type II: require ATP to either relax supercoiled DNA or introduce supercoils (gyrase in bacteria) Compounds that inhibit topoisomerases are used in...
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This note was uploaded on 07/08/2009 for the course LIFESCI LS 3 taught by Professor Paulolague during the Fall '09 term at UCLA.

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LEC03a - Figure 2.10 Melting temperature Temperature at which ½ of DNA molecules are denatured DNA molecules are denatured Beyond the double the

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