7. DNA replication 3 Flashcards
why are the 9-mer repeats on the oriC gene inverted?
because the ones that are in the forward direction here will code for the recognition sequence and on its antiparallel strand the backwards one will code for it as it will be forwards there (like opposites)
why are there so many A and T bases in the tandem array on the OriC gene?
A and T bases have fewer hydrogen bonds than G and C. therefore these bases will split apart easier which is needed to begin replication.
what is DNAA?
a protein that inititates replication in bacteria. it initiates unwinding of DNA at OriC
where does DNAA come from?
its accumulated during celluar replication and celluar growth
what does DnaA intitiate when on the OriC site?
- what does it form?
- what other things does it get
it forms a complex of proteins and these groups of proteins bind onto the 9-mer repeats.
how is cell replication regulated with DnaA?
DnaA is a protein thats only formed during gene expression. therefore once its used up to initiate replication with the cell, it cant be used again to contiue replicating more unil there is more DnaA made. positive feedback loop.
what happens when all the 9-mer receptors for protein complex’s are filled?
having all site bound causes DNA twisting to form loops. These loops cause a lot of strain on the DNA strand which result in melting the 13-mer region and breaking the A-T hydrogen bonds.
the two DNA strands seperate.
what do the DnaB proteins (helicase) do when they bind to the melted 13-mer sequence
helicase unwinds the DNA.
binds to either end of the melted region and forms the replication fork
what is DnaC?
helicase loading factor. it gives energy to helicase (DnaB) and delivers ATP for replication
in the intitiation of the leading and lagging strand, where does the primase bind too and what does it do?
primase (made by an RNA primer) binds to the helicase
it primes the 3’ end of the DNA and adds a nucleotide on to begin replication be DNA pol3
what do single stranded binding proteins do?
they attach to single stranded DNA and protect it from being degraded
label these subunits for the polymerase 3
what is the structure and funciton of the B-clamp subunits?
structure: a ring shaped clamp with a hole in the middle to accomidate the double helix of DNA
funciton: forms a ‘sliding clamp’ on the DNA as its replicated. prevents the polymerase from dissociating
how does DNA polymerase replicate DNA on the leading and the lagging strand at the same time?
DNA pol3 has two catalytic sites for each strand
there is a looping of the molecule - okazaki fragment will be close to the leading strand.
what does DNA gyrase do?
helps the overwinding that occurs when two strands are seperated. it helps positive super coiling by snipping part of the DNA.
its a type of topiosomerase
what do topiosomerase do and why?
make transient breaks in the DNA strand to allow them to unwind, then stick them back together.
to prevent the supercoiling that occurs due to helicase and gyrase
what are three features of replication in eurkaryotes and prokaryotes?
eukaryotes have many origins of replication of the chromosome
replication is bi-directional
