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DNA Replication and Repair

DNA Replication and Repair. The Central Dogma of Molecular Biology. T. A. A. A. A. T. A. T. T. T. T. A. G. C. G. C. C. C. C. G. G. G. G. C. A. A. T. T. T. T. A. A. A. A. T. T. T. A. A. A. A. T. A. T. T. T. T. A. C. G. G. G. G. C. G. C. C.

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DNA Replication and Repair

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  1. DNA Replication and Repair

  2. The Central Dogma of Molecular Biology

  3. T A A A A T A T T T T A G C G C C C C G G G G C A A T T T T A A A A T T T A A A A T A T T T T A C G G G G C G C C C C G DNA Replication • genetic information is passed on to the next generation • semi-conservative

  4. Overview of replication

  5. Review of DNA structure • double helix • each strand has a 5’ phosphate end and a 3’ hydroxyl end • strands run antiparallel to each other • A-T pairs (2 H-bonds), G-C pairs (3 H-bonds)

  6. STEP 1 Initiation at origins of replicationseparation sites on DNA strands • Depend on a specific AT-rich DNA sequence • Prokaryotes – one site • Eukaryotes – multiple sites • Replication bubble • Replication fork • Proceeds in two directions from point of origin

  7. The proteins of initiation • Helicase – unwinds double helix • Single-strand binding proteins – holds DNA apart

  8. STEP 2 Priminginitiation of DNA synthesis by RNA RNA primers bind to unwound sections through the action of primase • leading strand – only 1 primer • lagging strand – multiple primers • replaced by DNA later

  9. STEP 3Elongation of a new DNA strandlengthening in the 5’ 3’ direction DNA polymerase III can only add nucleotides to the 3’ hydroxyl end Leading strand • DNA pol III – adds nucleotides towards the replication fork; • DNA pol I - replaces RNA with DNA Lagging strand • DNA pol III - adds Okazaki fragments to free 3’ end away from replication fork • DNA pol I - replaces RNA with DNA • DNA ligase – joins Okazaki fragments to create a continuous strand

  10. STEP 4Proofreadingcorrecting errors in replication Mismatch repair • DNA pol III – proofreads nucleotides against the template strand Excision repair • nuclease – cuts damaged segment • DNA pol III and ligase– fill the gap left Telomeres at 5’ ends of lagging strands • no genes, only 100 – 1000 TTAGGG sequences to protect genes • telomerase catalyzes lengthening of telomeres

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