Topic 14, replication II.ppt.edu

Topic 14, replication II.ppt.edu - Topic 14: DNA...

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Topic 14: DNA replication part 2
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Learning objectives See topic 13 Be able to explain the problems associated with having a linear DNA genome (like the human genome) Be able to explain and/or diagram how human cells deal with the problem of preserving the ends of the chromosomes
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More replication enzymes to know: DNA Polymerase III DNA Polymerase I Topoisomerase I Rnase H Ligase Telomerase
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DNA polymerase III: I do almost all of the work around here! Exists as a dimer (2 copies that are physically associated) One copy does all of the work on the leading strand One copy does a lot of the work on the lagging strand Proofreading capacity: detects mistakes (a.k.a. mismatched base pairs), cuts them out, fixes them
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DNA polymerase I: I may be slow, but you can’t live without me! Only 1 copy per replication fork Only works on extending the Okazaki fragments on the lagging strand Primary job is to fill in the gaps as RNA primers are removed Same proofreading capability as DNA pol III
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What to do with all of these small DNA fragments that are synthesized? --Rnase H removes all RNA except last RNA nucleotide --DNA polymerase I removes last RNA nucleotide --DNA polymerase I fills in the gap with DNA --DNA ligase makes phosphodiester bond to seal DNA fragments together --End result is a continuous strand of DNA in which original fragments cannot be detected
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Ligase seals the deal Ligase requires energy stored in ATP for this reaction
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Topoisomerase I: Let me help you relax -As the DNA gets unwound in one stretch, it has to get overwound in another stretch.
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Topic 14, replication II.ppt.edu - Topic 14: DNA...

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