Lecture 12: DNA Replication

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Lecture 12 DNA Replication
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Outline

• Replication mode
• Basic mechanism and machinery
• Prokaryotes vs eukaryotes

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Replication mode

• semiconservative ---gt
• each strand becomes a template
• for new one
• conservative -----gt
• two parental strands become templates for
• new set of strands
• dispersive -----gt
• portions of parental strands are mixed
• with newly synthesized set of strands

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Replication mechanism (slow motion I)
1. Replication of origin --- DNA helicase
2. Primase
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Replication mechanism (slow motion II)
3. DNA polymerase III
4. Leading strand Lagging strand
discontinuous extension ----gt Okazaki fragment
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Replication mechanism (slow motion III)
5. Removal of primes and followed by DNA
ligation DNA pol I DNA ligase
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Replication mechanism
Origin of replication DNA helicase Primase
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Replication mechanism

• DNA polymerase III
• 5-3 direction
• DNA replication -bidirectional
• Leading and lagging strands
• Okazaki fragments
• DNA polymerase I removes
• remaining primers
• DNA ligase connects
• Okazaki fragments in lagging
• strands

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Enzymes for Replication

• DNA helicase
• Primase
• DNA polymerases (I, II, III)
• three activities 5-3 polymerase
• 5-3
  exonuclase activity (removal of primer)
• 3-5 exonuclase
  activity (proofreading)
• DNA ligase
• DNA topoisomerase

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Replication in circular DNAs
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Announcement for review and homework

• Need to pick up the homework for this week
• Michelle will have the review session for the
  second exam
• Monday 140-230 PM at LSB annex auditorium
• Exam2 will be reviewed in the discussion session
  for the nextweek