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Unformatted text preview: 3’ direction 5’ 3’ 3’ 5’ The leading strands are continually made as the replication fork proceeds But we need to synthesize DNA behind them! 3 9/21/10 5’ 3’ 3’ 5’ 5’ 3’ 3’ Comparing Leading Strand and Lagging Strand 5’ 5’ 3’ 3’ 5’ Lagging strand synthesis --> “Okazaki fragments” 1000 - 2000 nucleotides long in E. coli 100 - 200 nucleotides long in eukaryotes In this illustration: DNA polymerase I removes the RNA primer from the 5’ end of Okazaki fragment 2 and replaces it with DNA Important to note: The enzyme is using fragment 3 as the “primer” for synthesizing DNA Next steps: •  A different DNA polymerase (DNA Pol I) removes the RNA primer and fills in DNA sequence •  DNA ligase creates covalent bonds between the fragments (generating a continuous polymer) 5’ 3’ 4 9/21/10 Problem at the end of linear chromosomes Problem at the end of linear chromosomes The “lagging strand” of linear chromosomes should get shorter with every replication. Solution: Telomeres No primer for DNA polymerase: This last sequence can’t be filled in!! Te...
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This document was uploaded on 10/24/2013.

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