DNA Replication Flashcards
Why are the parent strands antiparallel during synthesis?
So they can be synthesised continuously.
What synthesises the primer?
DNA primase
What diseases are caused by mutations in DNA helicase?
- Werner syndrome: premature ageing. no replication
- Bloom syndrome: cancer, no sunlight.
What is needed for Okazaki fragments to be synthesised?
DNA primase
DNA polymerase
Ribonuclease (removes primase)
DNA polymerase to seal the gap
DNA ligase to seal the nick
What do DNA topoisomerases do?
Prevent DNA from becoming tangled during DNA replication.
As DNA unwinds, tension is created in the helix
Topoisomerases nick the strand and reseal to release the tension.
What types of topoisomerases are there?
Type I - seals and nicks 1 strand, no ATP required
Type II - Seals and nicks 2 strands, ATP required.
How many origin of replications are there in E. coli, yeast, and humans?
E. coli - 1
Yeast - 600-700
Humans - 100,000+
How is initiating replication in eukaryotes biphasic?
Two phases:
1. Replicator selection occurs in G1
2. Origin activation occurs in S phase
Why is replication in eukaryotes biphasic?
Temporal spatiation ensures each chromosome is only replicated once per cell cycle.
What happens in the biphasic replication:
ORC binds to replicator sequence, helicase proteins load onto ORC
High levels of Cdk
Activated RC
What do high levels of Cdk in initiating replication ensure?
No new RCS formed, activation of RC
What does a telomerase do?
Telomerase adds telomeres to the end of strands because primers have been removed and to prevent shortening because of this.
What is the telomerase shuffle?
3 nucleotides added
Moves forward 6 nucleotides
6 nucleotides added
Moves forward 6 nucleotides.
