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![Page 1: 1 Replication of the Genetic Material Genetic material must be duplicated for transfer into daughter cells. Complementary double-stranded DNA makes this.](https://reader030.fdocuments.in/reader030/viewer/2022032523/56649d8d5503460f94a75077/html5/thumbnails/1.jpg)
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Replication of the Genetic Material
Genetic material must be duplicated for transfer into
daughter cells.
Complementary double-stranded DNA
makes this possible
A
A
A
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Possible Mechanisms for DNA Replication
Which is correct?
semiconservative conservative dispersive
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Meselson - Stahl Experiment (1958)
Nitrogen isotopes
Density gradient centrifugation - CsCl
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Meselson - Stahl Experiment
Definitely not conservative
Results also consistent with dispersive
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Meselson - Stahl Experiment
Supports only semiconservative model
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Replication of DNA in Eukaryotic Chromosomes
How is DNA arranged and replicated?
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Replication of DNA in Eukaryotic Chromosomes
Taylor, Woods, and Hughes (1958)
CHO harlequinchromosomes
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DNA Polymerase Chain Elongation
Chain growth - 5’ to 3’ direction
3’ 5’ 5’ 3’
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DNA Polymerase Chain Elongation
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Replication Origin
Bidirectional Replication from Origin
Single origin in
Prokaryotes
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Replication Origins - Replicons
Multiple origins in Eukaryotes
Replicons
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Primer Requirement
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Initiation of DNA Replication - E. coli
Initiator protein DnaA binds oriC
denaturation
DNA helicases unwind DNA
DNA primase makes primers
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Replication Fork - Okazaki Fragments
Initial primers
Repriming
Discontinuous synthesis Lagging strand
Continuous synthesisLeading strand
5’
5’3’
3’
5’
3’
5’
3’
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Activities of DNA Polymerases
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Types of DNA Polymerases
E. Coli DNA polymerase I - single polypeptideDNA polymerase III - three polypeptide holoenzyme
Both capable of chain growth and 3’-5’ exonuclease activity Only pol I has 5’ - 3’ exonuclease activity
Eukaryotes
> 15 polymerases, 3 involved in replication of nuclear DNA
pol - with primase, creates RNA/DNA primerpol and pol - extend primers on leading/lagging strand
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Joining of Okazaki Fragments
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DNA Replication in E. coli (Fig. 3.6)
Initiation
Elongation
Primer Removal
Ligation
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DNA Replication in E. coli
Figure 3.8. Replisome Model. DNA pol III on lagging-strand templateis finishing synthesis of an Okazaki fragment.
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Telomere Problem
Due to:Linear chromosomes & Requirement for RNA primers
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Resolving the Telomere Problem
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Rolling Circle Replication
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Rolling Circle Replication in Phage