DNA Replication, Repair and Recombination 1 (Lec 3) Flashcards
What is the error rate in DNA replication?
1 mistake in every 10^9 base pairs.
True or False?
Germ cells have to have low mutation rates to maintain the species.
true
Why do somatic cells need low mutation rates?
to avoid uncontrolled proliferation/cancer
What reaction does DNA polymerase catalyze?
DNA synthesis
(DNA)n residues + dNTP -> (DNA) n + 1 residues + P2O7 ^4-
How is the DNA template directed?
new chain is assembled in a preexisting DNA template that is complementary to the incoming bases
True or False?
DNA replication requires dATP, dGTP, dCTP and dTTP
true
DNA polymerase requires a primer with a free ___ to begin
3’ -OH
What is the direction of growth of DNA?
5’ to 3’
Explain how the replication fork is asymmetric
Both strands are simultaneously replicated, DNA polymerase can only synthesize DNA in the 5’ to 3’ direction, leading strand is synthesized continuously, lagging strand is synthesized in segments
Where does the first step of proofreading occur?
just before a new nucleotide is added: enzyme must tighten its “fingers” around the active site, which is easier if the correct base is in place
When does exonucelolytic proofreading occur?
takes place immediately after incorrect base is added
What does 3’ to 5’ exonuclease do during proofreading?
clips off unpaired residues at 3’ primer terminus
How does 5’ to 3’ replication allow efficient error correction?
high energy bond is cleaved providing the energy for polymerization
How is the lagging strand synthesized?
backstitching process: DNA primase synthesizes a new RNA primer, DNA polymerase adds to new RNA primer to start new okazaki fragment, DNA plymerase finishes fragment, old RNA primer erased and replaced by DNA, nick sealed by DNA ligase
What is the protein at the DNA replication fork that unwinds DNA?
helicase
note: hydrolizes ATP which causes conformational change that propels it like a rotary engine along single stranded DNA