Replication

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Replication
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Central Dogma of Information Flow
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Wagging the Dogma
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Replication

• Replication- the synthesis of DNA using itself as
  a template.
• Three stages Initiation, Elongation, Termination

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Replication is Semiconservative

• Meselson-Stahl Experiment

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Initiation
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Replication Begins at a Specific Place Each Time

• Origin of replication (ori)

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Replication is Bidirectional

• Theta structure

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DNA Must be Uncoiled Before Replication

• Helicase
• ssb

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Replication is 5 - 3
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Okazaki Fragments are Used to Synthesize the
Lagging Strand
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Primers are Needed for Synthesis

• Primase

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Elongation

• Reaction

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Termination

• Least well understood

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Review of Replication - Initiation

• Ori bound by helicase and SSB (other proteins at
  site)
• Replication bubble forms
• primase and DNA polymerase III join complex
• Okazaki fragments used on lagging strand
• synthesis is 5 to 3

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Review of Replication - Elongation

• PPi product
• polymerase I removes RNA and fills gap

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Review of Replication - Termination

• Ligase seals nick (ATP dependent)
• Topoisomerase supercoils DNA (cut, wrap, ligate)

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Proofreading

• 1 mistake every 105 - 106 bases during
  replication (3 - 5 exonuclease activity)
• In DNA, 1 mistake every 108 - 109 bases
• other repair mech. must exist

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Repair Mechanisms

• Mismatch repair
• Base Excision repair
• Nucleotide Excision
• Direct Repair

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In Eukaryotes, the Major Differences are the
Numbers and Names of the Molecules

• Prokaryotes Eukaryotes
• 1 ori and ter multiple ori and ter
• Polymerases III and I Pols d and a
• Okazaki fragments 1000 100-250 nt
• supercoiling histones