LECTURE 08 DNA Replication

LECTURE 08 DNA Replication - 2:010 Principles of Biology...

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2:010 Principles of Biology Lecture 8 DNA Replication Last lecture we demonstrated that DNA is the genetic material. This means that every time a cell divides all the DNA must be replicated because each daughter cell must receive all of the genetic material. Is there anything we can deduce about DNA replication by examining its structure. Watson and Crick won the Nobel Prize for the determination of the double helix structure of DNA. - 2 complementary strands - Nucleotide base from one strand H-bonded to a base on the other strand. - A-T and G-C This structure also led them to hypothesize a mechanism for the replication of DNA. a) Break the H-bonds between the nucleotide bases and separate the parental DNA strands (dark blue) . b) Each parental strand serves as a template for determining the order of nucleotides along new daughter strands (light blue) . c) Covalent bonds are formed between the deoxynucleotides to make the sugar- phosphate backbone of the daughter strand complementary to the parental strand. d) 2 DNA molecules are formed each containing one parental strand and one 1
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daughter strand. This mode of replication is considered to be semi-conservative. However, it is not the only way that DNA could be replicated given its specific structure. 1. In a conservative model of replication the 2 parental strands, after acting as templates hybridize together. The original DNA is reformed and the new DNA has 2 daughter strands. After a second round of replication there will be 3 double stranded helices of DNA all made of new deoxynucleotides and the one original DNA molecule. 3. In a dispersive model of replication each copy of DNA consists of mixtures of parental and newly synthesized strands. New DNA is dispersed throughout each strand of new DNA molecules. After 2 generations of replication all the DNA molecules will be mixed. 2. In the semi-conservative model after 2 rounds of replication half the molecules of DNA will be mixed and half will be all new. Therefore, in order to distinguish between these models we have to examine at least 2 rounds of replication. This was done in classical experiments –performed by Meselson and Stahl in 1958. - They grew bacteria in a medium that would 2 CONSERVATIV E DISPERSIVE SEMI-CONSERVATIVE
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label the DNA.
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This note was uploaded on 03/30/2008 for the course BIO 2:010 taught by Professor Denburg during the Spring '08 term at University of Iowa.

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LECTURE 08 DNA Replication - 2:010 Principles of Biology...

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