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DNA Replication

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Conservative replication an entirely new double stranded DNA molecule is produced ... Proteins Involved in DNA Replication. Presynthesis. Topoisomerase ... – PowerPoint PPT presentation

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Title: DNA Replication


1
DNA Replication
  • The reason why most of us dont have three eyes.

2
The Three Requirements of Genetic Material
  • Must be able to replicate.
  • Must control the expression of traits.
  • Must be able to change in a controlled way.

3
DNA Replication
  • What is DNA Replication?
  • How fast does DNA replicate?
  • How does DNA replicate?
  • Whats amazing about DNA replication?

4
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5
Conservative replication Semiconservative
replication Dispersive replication
6
DNA Replication
  • Three Models
  • Conservative replication an entirely new double
    stranded DNA molecule is produced
  • Semi-conservative replication each strand
    serves as a template for assembly of a new
    complementary strand
  • Dispersive replication breakage in both
    parental strands and reassembly

7
Meselson-Stahl Experiment
  • 1957, Matthew Meselson, Franklin Stahl,
    California Inst. Of Technology
  • Heavy nitrogen 15N
  • Shift to 14N
  • Determine buoyant density in CsCl gradient

Time
DNA replicates in a semiconservative fashion
8
What is DNA Replication?
9
How Fast is DNA Replication?
  • Facts
  • In prokaryotes (E. coli) about 1000 bases per
    second.
  • E. colis genome is 4.7 X 106 bases
  • In eukaryotes - about 50 nucleotides per second.
  • Average human chromosome has 150 X 106 bases.
  • Answer
  • Pretty darn fast?
  • Not fast enough?

10
Proteins Involved in DNA Replication
  • Presynthesis
  • Topoisomerase
  • Single-stranded binding proteins
  • Helicase
  • Synthesis
  • Primase
  • Polymerase
  • Exonuclease
  • Ligase

11
http//www.johnkyrk.com/DNAreplication.html
12
Presynthesis Replication Proteins
  • Topoisomerase - an enzyme responsible for
    creating a nick in a strand of supercoiled DNA,
    relaxing the helix. There are four types that
    fall into two main groups.
  • Helicase - an enzyme that unwinds DNA.
  • Single-stranded binding proteins attaches to
    the unwound single strand of DNA to stabilize it.
    Speeds up DNA replication.

13
Proposed 3-D Models of Topoisomerase I and II
from the Protein Data Bank.
14
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15
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16
DNA Replication Requires Enzymes
  • Primase an enzyme that attaches an RNA primer
    to the single stranded DNA.
  • DNA Ligase forms a covalent link between the 3
    OH and 5 phosphate groups

17
DNA Primase
  • Role synthesis of short RNA primers on single
    stranded DNA templates (every 500 2,000
    nucleotides on the lagging strand).
  • Three domains
  • N-terminal zinc-binding motif.
  • Central region with RNA polymerase sequence
    homology.
  • C-terminal residue that interacts with helicase.

18
DNA Polymerase
Synthesis Proofreading Error Correction
19
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20
DNA Polymerase
  • DNA Polymerase I (Pol I) first enzyme discovered
    with polymerase activity, best characterized
    enzyme
  • 5' to 3' elongation (polymerase activity)
  • 3' to 5' exonuclease (proof-reading activity)
  • 5' to 3' exonuclease (repair activity)
  • DNA Polymerase II (Pol II)
  • Repairs gaps, 5 3
  • DNA Polymerase III
  • Provides the primary 5 to 3 polymerase activity
  • Slight exonuclease activity.

21
DNA Replication Summary
  • http//www.ncc.gmu.edu/dna/replicat.htm
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