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16_Lecture_Part2_post - DNA Replication: Getting Started...

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DNA Replication: Getting Started The copying of DNA is remarkable in its speed and accuracy More than a dozen enzymes and other proteins participate in DNA replication Replication begins at particular sites called origins of replication , where the two DNA strands are separated, opening up a replication “bubble” A eukaryotic chromosome may have hundreds or even thousands of origins of replication Replication proceeds in both directions from each origin, until the entire molecule is copied
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Figure 16.12a (a) Origin of replication in an E. coli cell Origin of replication Parental (template) strand Double- stranded DNA molecule Daughter (new) strand Replication fork Replication bubble Two daughter DNA molecules 0.5 m
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Figure 16.12b (b) Origins of replication in a eukaryotic cell Origin of replication Double-stranded DNA molecule Parental (template) strand Daughter (new) strand Bubble Replication fork Two daughter DNA molecules 0.25 m
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At the end of each replication bubble is a replication fork , a Y-shaped region where new DNA strands are elongating Helicases are enzymes that untwist the double helix at the replication forks Single-strand binding proteins bind to and stabilize single-stranded DNA Topoisomerase corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands
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Topoisomerase Primase RNA primer Helicase Single-strand binding proteins 5 3 5 5 3 3
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An enzyme called primase can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template The primer is short (5 10 nucleotides long), and the 3 end serves as the starting point for the new DNA strand DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to the 3 end The initial nucleotide strand is a short RNA primer
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Synthesizing a New DNA Strand Enzymes called DNA polymerases catalyze the elongation of new DNA at a replication fork Most DNA polymerases require a primer and a DNA template strand The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells
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Each monomer that is added to a growing DNA strand is a nucleoside triphosphate dATP
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This note was uploaded on 04/30/2011 for the course BIOL 1362 taught by Professor Loeblich during the Spring '08 term at University of Houston.

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16_Lecture_Part2_post - DNA Replication: Getting Started...

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