DNA REPLICATION Flashcards
3 steps of prokaryotic replication
- Initiation
- Elongation
- Termination
Prokaryotic initation
DNA Pol III initiates from a single replication origin called oriC
Structure of DNA Pol III
a) CORE enzyme
b) gamma complex
c) epsilon subunit
d) funny t sub unit
e) beta subunit
a) alpha sub unit (5’ - 3’ polymerisation)
sigma sub unit (proof reading exonuclease)
theta core assembly
b) 5 sub units for loading and unloading polymerase onto DNA template via a clamp
c) used as a proof reading subunit - exonuclease
d) connects two polymerase alpha sub units to create dimeric polymerase unit
e) sliding clamp to tether polymerase to the dna
How are RNA primers synthesised?
DNA primase
Function of DnaB helicase
in prokaryotic initiation it separates the strands
How does prokaryotic DNA replication occur?
- DnaA- ATP proteins recognise oriC and DnaB helicase unwinds strands
- held apart by single stranded binding proteins
- RNA primase synthesises primers
- DNA Pol III polymerises strands
Replication of the leading strand (5’ - 3’) is ______
Continuous
Replication of the lagging strand is _____, producing ____ fragments.
discontinuous
Okazaki
What slows polymerases
Fork traps
Why is lagging strand looped around?
Both polymerases need to function in the same direction and simultaneously
What removes RNA primers?
DNA pol II using its exonuclease action in a 5’ to 3’ direction
What seals gaps?
DNA ligase
What does DNA pol I do?
maturation of Okazaki fragments
Why is eukaryotic replication different?
- Humans have 3 billion bp compared to E.coli 30 million
- therefore humans have multiple origins of replication
- chromatin disassembly
- telomeres are used to protect DNA from exonuclease action
Why do telomeres shorten?
- Eukaryotes have difficulty replicating their linear chromosomes completely - ‘the end replication problem’
- telomerase extends 3’ end of chromosomal DNA by a G-rich repeat, to counteract loss of DNA by incomplete replcation
