DNA replication Flashcards
where does DNA replication start
at the origin of replication
when does it have to occur
before every cell division
basic explanation of DNA replication
H-bonds are broken
parent strands unwind and seperate
each chain acts as a template for the synthesis of a new complementary daughter strand
DNA replication is semi-conservative
each daughter molecule consists of one old strand and one new strand
what are origins of replication ?
position at which DNA is 1st opened
how many ORI in prokaryotes ?
1
how many ORI in eukaryotes ?
10,000
replication is bidirectional
2 replication forks are formed from each ORI
replication forks move away in both directions
proceeds until entire molecule is copied
what direction is DNA synthesised in
5’ to 3’
what provides the energy for the condensation rxn that links the monomer to the chain and releases pyrophosphate
hydrolysis of one phosphoanhydride bond in the nucleoside triphosphate
what does DNA polymerase require
a template and a primer
what can an RNA polymer called primase do?
can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template
what does the 3’ end of the RNA primer serve as ?
the starting point for the new DNA strand
DNA POl 1
single polypeptide chain that has 3 activities associated with it -
5’ exonuclease
3’ exonuclease
polymerase
exonuclease
enzyme that removes nucleotides from an end of a DNA strand
3’ degrades from 3’ end and 5’ from 5’ end
DNA Pol 2 `
single polypeptide chain that has 2 activities associated with it
3’ exonuclease and polymerase
what are the three stages of DNA replication
initiation
elongation
termination
initiation
at ORI
helicase unwinds the helix in both directions
creates 2 replication fork
single stranded binding protein bind the unwound DNA and stabilises it
elongation
strand that is synthesised continuously is the leading strand
strand that is synthesised discontinuously is the lagging strand
which is a major DNA replication enzyme DNA polymerase 3 or DNA polymerase 1
DNA polymerase 3
leading strand synthesis
one primer is synthesised
DNA pol 3 adds DNA nucleotides to the new strand
DNA polymerase synthesises a leading strand continuously
DNA pol 1 removes the RNA primer
DNA pol 1 fill in gap using 5’-3’ pol activity
what catalyses the phosphodiester bond
DNA ligase
Lagging strand synthesis
each Okazaki fragment has its own primer
DNA polymerase 3 extends from 3’ end of each RNA primer
DNA pol 3 stops at RNA primer leaving a gap and RNA in the molecule
DNA pol 1 fills in gap using 5’-3’ polymerase activity
what enzyme is self correcting
DNA polymerase
