what is topoisomerases and what does it do ?
is an enzyme that is decatinating the (interlocking of the DNA circles) to relax
why must we use toperisomers and relax DNA ?
to relieve torsional stress
what is type 1 topoisomerase ?
it works in an ATP independent(no ATP) manner to unwind DNA
what is the difference between type 1 topoisomerases in Eukaryote vs prokaryote ?
in euk it can be used for both positive and negative supercoiling
in prok it can be used in only for negative
how does bacterial topoisomerase 1 work ?
it binds to the negative wound DNA and unwinds it by creating a transient SINGLE strand break
what is type 2 toperisomerases and how is it in euk and prok
type 2 is atp dependant (need ATP) and can relax both negative and postive in both pro and euk
how does bacterial topoisomerase 2 work?
it forms a dimer upon atp binding that allows for cleavage of the transient DOUBLE strand breaks
Comparing bacteria and Eukaryotes and prokaryotes how many origins of replication do we have ?
in prokayrote there are 1 oric
in eukaryotes there are many; some active , some inactive
within eukaryotes where is the origin of replication ?
we dont have the consensus sequences that defines our origin of replication
what 2 things is the rate of genome replication affected by ?
- number of origins
- the rate at which the origins are initiated
where in the nucleus is replication occuring euk ?
in replication factories where active replication forks are clustered in subnuclear compartments
what are the 4 steps to creating and active replication fork euk and where does it occur in the phases?
- Chromatin must be opened up and the histones removed
- OrC ( origin recognition complex) and Cdc6 must bind to the origin and get a single helicase MCM-27
- protein like Cdc 45 and GINS must be loaded and it forms the pre initiation complex
- Cdc 45, MCM-27 and GINs are turned into a active helicase CMG. and are on the leading strand
what is replication licensing euk ;why must eukaryotes separate ORC from replication licensing ?
regulated by CDK. to prevent DNA from replication multiple times
what 2 roles does MCM2-7 have in the CMG complex ?
is a licensing protein and a helicase
when happens when CDK activity is low ?
Mcm-27 is loaded on the origin
what happens when CDK activity is high?
the licensing origin is fired and it phosphorylates mcm 2-7
in what direction does the CMG helicase move and on what strands
it moves 3-5 on the leading strand
what lays down the RNA primer and how
DNA pol alpha by biding to the initiation complex
what is polymerase switching ?
where DNA POL alpha (a) is switched onto the lagging strand for DNA pol s and DNA pol e is on the leading strand for replication
what is the sliding clamp of euk and what is it for and how is it used ?
pcna is for preventing dna pol loose it place ;PCNA is the sliding clamp for euk and it is loaded onto the DNA RFC via atp
how is proofreading and termination done in dna replication
though high fidelity DNA. pol a s and e that has minimum errors
what are the 5 steps done after termination?
- removal of RNA primer
- filling of gaps
- okazaki frags on lagging strand must be joined
- dna pol s cause strand displacement
5.FEN-1 removes RNA 5 flap
what does DNA ligase do ?
join the ends of the okanzaki frags
