Origin Of Replication Flashcards
Replicon
All the DNA replicated from a single ori
What are origins of replication?
Specific sites where DNA unwinding and initiation of replication begins
Replicator
Cis-acting sequence required to initiate replication
ORIs are part of the replicator sequence
Initiators
Recognize DNA element in replicator and initiate replication
sequence specific usually
9-mer
Site of DnaA binding
13-mer
A-T rich
DnaB
Helicase
DnaC
Helicase loader
Replication in E. coli - (12points)
- DnaA binds to 9-mer
- When bound to ATP, DnaA can also bind to 13-mer
- DNA double strands begin to separate
- DnaB and DnaC recognize and bind to DnaA
- DnaC also recognizes ssDNA
- Each DnaB recruits a primase
- Primer formation begins and causes DnaC release and DnaB activation
- DnaB movement removes any remaining DnaA
- DNA pol holoenzyme clam loaders recognize primers and helicase
- DNA pol recognizes primer template junction on leading strands
- Leading strand synthesis starts followed by lagging strand
- Each replication will continue until it reaches the end of the template or meets another replication fork
Finishing replication in prokaryotes
- Prokaryotes have circular genomes
- Process of replication results in linked daughter genomes (catenane)
- Topoisomerase II decatenanates daughters
Replicators in multicellular organisms
- Mutational assays to knock out function of replicators do not work
- Thus likely that specific DNA sequences for replicators in multicellular organism
- Reduced local nucleosome density and nearby transcription are important
Not well understood
During which part of the cell cycle does the helicase loading occur?
G1
What activates helicases?
Protein kinases
What inhibits helicase loading?
CDK
Telomeres
Short pieces of DNA that protect chromosome ends
They do not code for protein
