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DNA Replication, Repair, and Recombination

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DNA polymerase is responsible for copying and repairing DNA. DNA replication is asymmetrical. One strand of DNA is always retained during replication ... – PowerPoint PPT presentation

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Title: DNA Replication, Repair, and Recombination


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  • DNA Replication, Repair, and Recombination

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  • Mutations are substitutions, deletions or
    additions in a DNA sequence
  • Many mutations are bad and eliminated by natural
    selection
  • Life requires that the mutation rate be low.
  • DNA replication must ensure that the mutation
    rate is low

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  • DNA polymerase is responsible for copying and
    repairing DNA
  • DNA replication is asymmetrical
  • One strand of DNA is always retained during
    replication
  • DNA polymerase moves along the DNA in the 5 to
    3 direction always

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  • As DNA polymerase moves along the DNA template
    the two strands of DNA separate forming a
    replication fork.
  • The replication fork has a leading strand and a
    lagging strand. Replication along the leading
    strand is continuous while it is discontinuous
    along the lagging strand

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  • The lagging strand consists of short DNA
    sequences known as Okazaki fragments.
  • The Okazaki fragments are joined together by DNA
    ligase

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  • The mutation rate of DNA replication is one nt in
    nine billion nts
  • DNA polymerase has a proof reading activity to
    ensure that the correct nt is added
  • Before DNA polymerase can catalyze the covalent
    bond between nts it must undergo a conformational
    change.

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  • Exonucleolytic proofreading occurs after an
    incorrect nt has been covalently bonded to a DNA
    strand
  • DNA polymerase requires a base paired 3 OH to
    add nts.
  • If a mismatch has occurred then the DNA
    polymerase cannot move along the DNA template
  • DNA polymerase has a requirement for a base
    paired primer to proceed.

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  • The 3 to 5 proofreading exonuclease removes
    unpaired nts from the growing DNA strand.

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