9 - BIO 320: Lecture 9 DNA REPLICATION: DNA replication and...

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FACTS about DNA replication: 1) The enzymes that synthesize DNA (DNA polymerases) do so only in one direction (5'-3') . Each subsequent dNTP is added to the 3' OH group of an existing strand. 2) The requirement for a free 3' OH demands that a primer be annealed to the the template strand to initiate DNA replication. There are 'signals' within DNA that specify sites for the initiation of replication. Replication proceeds bi-directionally from these origins of replication. Circular chromosomes (e.g. bacterial) contain a single origin, eukaryotic chromosomes contain multiple origins ( Replication of a single human chromosome would take about 40 days if there were a single origin of replication ). 3) At a replication fork DNA synthesis on one strand can proceed continuously (the 3' to 5' strand). The other strand is synthesized dis-continuously (requiring multiple RNA priming events) and then subsequently pasted together. 4) The error rates are much lower than expected based on thermodynamic considerations. This is due to a number of factors, including proof-reading activity of polymerase, processivity factors and mismatch repair. 5' 3' 3' 5' ori ori 5' 5' 3' 3' 5' 5' 5' 3' 5' 3' 5' 5' 5' 3' Okazaki fragments The polarity of DNA synthesis causes another problem for the replication of the ends of linear DNA molecules -e.g. Question for thought. .. what is this problem?
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This note was uploaded on 06/03/2008 for the course BIO 320 taught by Professor N/a during the Spring '08 term at SUNY Stony Brook.

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9 - BIO 320: Lecture 9 DNA REPLICATION: DNA replication and...

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