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PABIO 551 -- Lecture 4

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PABIO 551 -- Lecture 4

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    1. PABIO 551 -- Lecture 4 DNA Replication Telomeres DNA Repair

    2. General features of DNA replication

    3. DNA replication is semi-conservative

    4. The Meselson – Stahl experiment

    5. Bidirectional replication bubbles

    6. Replication origins

    7. “Problems” in DNA replication DNA polymerases are unable to melt duplex DNA. All known DNA polymerases require a primer. The “lagging strand” problem. Different proteins solve these problems………….

    8. DnaA protein and strand melting

    9. Other proteins in DNA replication

    10. The lagging strand problem

    11. Synthesis of the lagging strand

    12. Major DNA polymerases in E. coli

    13. Other DNA polymerases

    14. Focus on DNA polymerase III…..

    15. Processivity of DNA polymerase and the ?-subunit dimer “clamp”

    16. The leading and lagging strands are synthesized concurrently

    17. Topoisomerase and DNA replication Enzymes that affect the topology (supercoiling and catenation) of DNA. Type I -- cleaves one DNA strand, relaxes supercoiling by one turn, then reseals. No energy required. Type II -- Cleaves both DNA strands, can relax or tighten; catenate/decatenate DNA. Requires energy input.

    18. E. coli Topoisomerase I in action

    19. Type II topoisomerases change DNA topology

    20. DNA replication comes to an end

    21. Telomeres

    22. Links between DNA repair and telomeres

    23. Telomerase……..

    26. DNA damage and repair

    27. Proofreading -- the first line of defense

    28. Types of repair systems

    29. Base excision repair Repairs damaged bases (deaminated, alkylated) that result in incorrect basepairing Damaged base is repaired DNA glycosylases Beaks the N-glycosidic bond to create and AP site AP endonucleases Recognizes site and nicks damaged DNA on 5 ´ side DNA pol 1 extends DNA from 3 ´OH

    30. Mismatch repair of single-base mispairs

    31. Excision repair of thymine dimers

    32. Excision repair of DNA by E. coli UvrABC

    33. Double stranded breaks – “the unkindest cut” A single DS break can be lethal. Repaired by: Homologous recombination. Information is present on the second chromosome. Can result in mistakes. Non-homologous end joining.

    34. End-joining repair of nonhomologous DNA

    35. Links between DNA repair and telomeres

    36. DNA damage, repair and cancer

    38. Example of Aims test

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