Symes DNA Replication Flashcards
OriC
Replication initiation region in prokaryotes
- 3 AT-rich sequences
- 4 9bp sites (DNAa binding domain)
DNAa
Initiatior proteins which binds causing the DNA to bend
- splits DNA apart
- binding mediated by positive histone-like proteins
- prokaryotic
DnaB/C
Helicase which displaces DNAa
- prokaryotic
SSBs
Stabilise ssDNA
- prokaryotic
DnaG
Part of the primosome, makes primers
- prokaryotic
Function of DNA Pol 1
Performs primer excision and DNA repair
- fills in gap left behind by primer
- prokaryotic
What does the 3’ exonuclease of DNA Pol 1 do?
Proofreading, removes wrong base
- prokaryotic
Function of 5’ exonuclease of DNA Pol 1
Removes primers (nick translation)
- prokaryotic
Nick Translation
5’ exonuclease removes primer one base at a time until it reaches DNA
- DNA Pol 1 fills in the gap
- DNA ligase then seals the gap
DNA Pol III
Performs the bulk of replication in prokaryotes
- high processivity and high rate
- prokaryotic
Subunits in core enzyme of DNA Pol III
Dimer of alpha, epsilon (3’ exo), theta
- prokaryotic
beta sliding clamp
Part of DNA Pol III
- improves processivity
- negative amino acids on the interior
- prokaryotic
Gamma complex
beta clamp loader
- chi subunit helps DNA Pol III transition form making RNA primer to making DNA
Replisome
Creation of a loop at the replication fork so DNA Pol III can go in the same direction on both strands
What perfroms proofreading in prokaryotes
Epsilon subunit of DNA Pol III removes the mismatched base with its 3’ to 5’ exonuclease
How does termination in prokaryotes occur?
ter and TUS proteins
- topoisomerase 2 then separates and relegates the interlinking strands
4 similarities between prokaryotic and eukaryotic replication
1) semi-conservative
2) Bi-directional
3) requires RNA primers
4) Leading strand and Okazaki fragments
Prokaryotic initiation mechanism
Initiation begins at a single initiation site with additional rounds started before completion of the first round
Prokaryotic Priming mechanism
Provides an unreacted 3’ OH to allow DNA Pol to bind
- RNA primer: 5-10 nts, made 5’ to 3’
DNA Polymerase Gamma
Found in the mitochondria
Eukaryotic
DNA Polymerase Beta
Responsible for DNA repair
Eukaryotic
DNA Polymerase alpha
Contains the primase, makes RNA Primer
- no proofreading
Eukaryotic
DNA Polymerase delta
What does it do?
Responsible for lagging strand replication
- combines with epsilon to fill in gap left behind by RNA primer
Eukaryotic
DNA Polymerase Epsilon
Responsible for leading strand replication
- combines with delta to fill in gap left behind by RNA primer
Eukaryotic
What happens to nucleosomes in eukaryotic replication?
Dissociate ahead of the fork, then resynthesize after it
Eukaryotic
ORC
Binds next to AT-rich regions to bend DNA
Eukaryotic
MCMs
Helicase
- mini chromosome maintenance proteins
Eukaryotic
RPA
SSBs
- Replication Protein A
Eukaryotic
PCNA
Beta-clamp
Eukaryotic
RFC
Clamp loader
- Replication Factor C
Eukaryotic
RNase H/Fen1
Removal of RNA primers
Eukaryotic
Licensing
Part of replication
- assembly of pre-replication complex on ARS
- pre-RC contains ORC, inactive MCMs, others
Eukaryotic
ARS
Origin of replication
Eukaryotic
Firing
Part of replication
- Helicase is activated, activating the RC
Eukaryotic
hTERT
Protein component of reverse transcriptase
hTR
Template for hTERT
- RNA component of reverse transcriptase
t-loop
Leftover overhang which comes in and displaces dsDNA to make a D-loop-t-loop
Dyskeratosis Congenita
Mutations in hTERT/hTR which cause premature mortality
- example of anticipation
Function of chi subunit of gamma subunit
Interacts with SSBs to transition DNA over to DNA Pol III for replication
Which polymerase does PCNA increase the processivity of?
Delta