dna replication 4 Flashcards
what does primase synthesise and when will it produce this
a rna primer when attached to helicase
how to we prevent the ssdna from reclosing up again
single-stranded binding protein will bind to prevent closing
what will ssb proteins form and why is this useful
a tetramer meaning the outermost ssb proteins will be easier to remove by the polymerases
what does the primer and the ssb protein trigger and where
the arrival of the pol III holoenzyme and at the 3’ end
what are the three parts of the pol III holoenzyme
pol III core, tau proteins, clamp loader
what does the clamp loader load onto the protein and what then binds to this
beta clamp, the pol III core binds to this
what detaches the beta clamp from the clap loader
atp hydrolysis
what is the beta clamp encoded by and what does it give to the poll II core
dnaN to produce a ring dimer
it gives processivity
what is formed when the pol III catches up to the helicase
replisome
what is a replisome, where is it located and how big is it
combination of the pol III holoenzyme and the primasome
it is at the replication fork
it is around 50 nm
why does the lagging strand start to loop back on itself
as more ssdna is created, it loops back and this allows the primer to work
when will the pol III core bind on the lagging stand
when enough ssdna has emerged
what does helicase and pol III form
trombone model
when will the Okazaki fragment stop being produced
when the poll III core meets the originally added primer which is 5’ to 3’ so it stops as it cannot process dna
what happens when the first Okazaki fragment is made and what happens to poll III core
primase will rebind and add helicase back on and adds on another primer
it will release the strand
what are the two enzymes that edit the lagging strand
pol I and dna ligase
what are the two proteins that allow termination
ter and tus
how do ter and tus work
they are orientation-specific, only allowing movement in one direction, once each strand gets to the centre it cannot continue
what happens when the fork reaches ter-tus complex in the wrong direction
helicase will stall
what removes the supercoiling until the last 200 bps
dna gyrase
what removes the final 200bps of supercoiling
topoisomerase 4
what adds methyl onto the GATC sequences and where does it add it
dam and onto the adenosine
what is the difference between an old DNA strand and a newly replicated one
old are both methylated
new is hemimethylated
what binds to a hemimethylated sequence and why is this important
seqA protein
- it prevents dnaA from binding and it binds this DNA to the membrane
what will happen to an unmethylated stand of dna
they will replicate normally
