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DNA replication in prokaryotes
- circular shape molecule, up to few mil. bps
- SINGLE origin of replication
- replication BIdirectional
- Both strands replicated simultaneously
- meeting/terminating at ter sites, producing 2 circular molecules
- about 20min
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DNA Replication in eukaryotes
- MULTIPLE LINEAR DNA molecules (1 per chromosome), each millions of bps
- Multiple ori's
- need special mechanisms to fully replicate ENDS of each molecule
- several hours
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Issues to be resolved during DNA replication
- 1. mechanism must exist for DNA to unwind and be STABLE in open position: helicase and ssBP
- 2. Unwinding and synthesis create tension further down helix which needs to be reduced: topoisomerases
- 3. Primer needs to be synthesized for polymerization to start: primase
- 4. Both strands synthesized simultaneously, but in different manners (continuous w/leading and lagging): DNA polymerase III, replisome, okazaki fragments
- 5. RNA primer must be removed prior to completion of replication: DNA polymerase I
- 6. Gaps between strands must be filled: ligase
- 7. DNA needs to be proofread for errors: DNA polymerase I and III
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