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DNA Replication

DNA Replication. Chapter 16. Review: History & Structure. Griffith’s experiment. Hershey & Chase’s Experiment. Avery, M c carty , & Macloed’s Experiment. Wilkins & Franklin’s Experiment. Chargaff’s Experiment. Watson & Crick. DNA Replication. Making DNA from existing DNA

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DNA Replication

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  1. DNA Replication Chapter 16

  2. Review: History & Structure

  3. Griffith’s experiment

  4. Hershey & Chase’s Experiment

  5. Avery, Mccarty, & Macloed’s Experiment

  6. Wilkins & Franklin’s Experiment

  7. Chargaff’s Experiment

  8. Watson & Crick

  9. DNA Replication • Making DNA from existing DNA • Semi-conservative • At the end of DNA replication, each daughter molecule has one old strand (from the parent DNA) and one new strand (synthesized during replication)

  10. DNA Replication • Step 1: • Helicases unwind DNA at origin of replication by breaking hydrogen bonds between nitrogen bases • Replication bubble forms as two parental strands separate • Replication fork forms at end of each replication bubble

  11. DNA Replication • Step 2: • Single-strand binding proteins hold theunpaired DNA strands apart while new DNA strands are being synthesized • Topoisomerase protein binds to parental DNA to relieve strain untwisting puts on replication fork

  12. DNA Replication • Step 3: • Primase creates a short RNA primer that binds to the parent DNA to signal DNA polymerase III where to begin adding nucleotides • RNA primer will later be replaced with DNA nucleotides

  13. Step 4: • DNA Polymerase III adds nucleotides to exposed bases in 5’-3’ direction at the RNA primer • Leading strand • Produced continuously in 5’-3’ direction • Elongation moves towards replication fork • Lagging strand • Produced in pieces • Okazaki fragments • Elongation moves in opposite direction of replication fork (5’-3’)

  14. Step 5: • Lagging strand is completed as DNA ligase seals Okazaki fragments

  15. Proofreading & Repair • Initial error rate in replication is 1 in 100,000 nucleotides • DNA polymerases proofread and correct errors • Error rate in completed replication is 1 in 10 billion bases

  16. Mismatch repair • For that 1 in 10 billion errors that escapes DNA polymerase or are due to environmental mutations • Many enzymes involved • Cut out damaged section (nuclease) • Replace with new nucleotides (DNA polymerase) • Seal in place (DNA ligase)

  17. Telomeres • As cells divide, chromosomes erode after multiple DNA replications • Telomeres • End caps of non-coding DNA that protect the coding genes on the chromosomes • Think of the plastic pieces on the ends of your shoelaces • These sequences shorten after each round of replication so the actual genes do not • Part of aging process?

  18. telomerase • Enzyme that lengthens the ends of telomeres in germ cells (give rise to gametes) • Prevents loss of critical genes in zygote • Cancer cells have mechanisms that activate telomerase to allow unlimited division without loss of DNA

  19. Animations • Bioflix animation • DNA replication cartoon

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