11-17-08_DNA_repairA_awoolley

11-17-08_DNA_repairA_awoolley - DNA Error Detection and...

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Can you do anything correctly one billion times in a row? DNA Error Detection and Repair
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DNA replication is semi-conservative Each new double helix consists of one new strand and one old strand
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Review of replication Replication in prokaryotes begins at a single origin site Origin is short DNA sequence recognized by multiple DNA binding proteins Replication moves out in both directions from origins in 5’ to 3’ direction of new strand Two replication forks moving in opposite directions At the replication fork, parent helix is separating Daughter strands are being synthesized Replication terminates when forks meet http://staff.jccc.net/pdecell/proteinsynthesis/dnareprokary.html
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Mechanical stresses of DNA unwinding: gyrases and ‘single strand binding proteins’ DNA gyrase travels along DNA ahead of fork removing positive supercoils
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View at the fork DNA helicases break the double helix into two single strands Single strand binding proteins prevent recoiling or reforming two strands
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Semidiscontinuous replication steps Polymerases only work on existing 3’ end with OH group. Need primase to create initial RNA primer for leading strand or multiple primers for lagging strand Lagging strand formed in multiple small 5’ to 3’ segments called Okazaki fragments . DNA polymerase III replisome sequentially elongates leading strand and lagging strand fragments in 5’ to 3’ direction DNA polymerase I replaces RNA primers between fragments with DNA DNA ligase joins Okazaki fragments
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The replisome machine A β -clamp encircles the DNA and keeps polymerase in proximity of DNA template DNA polymerase III stays on same β -clamp on leading strand. On lagging strand, polymerase goes from one fragment to the next and uses multiple clamps . Clamps are loaded around DNA by a clamp loader .
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Standard DNA Replication Animation http://www.gofish.com/player.gfp?gfid=30-1123745 Not bad…
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Good DNA Replication Animation http://www.youtube.com/watch (Replication @ 1:42 to 2:50) By Drew Berry at the Walter and Eliza Hall Institute of Medical Research, in 2003 (Also look for his ‘Apoptosis’ film)
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homologues in eukaryotes
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11-17-08_DNA_repairA_awoolley - DNA Error Detection and...

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