M1 L4 Flashcards
Examples of DNA repair polymerases
Lambda and mu
What is deamination
Loss of N group, which gets replaced by an oxygen
What does a deaminated cytosine become
U (an RNA base)
What does deaminated met-C become
Thymine
What is an abasic site
where a base is lost
What causes the formation of an abasic site
oxidative damage, deamination and spontaneous loss of a base
How can DNA damage become a permanent mutation
The DNA damage leads to the wrong base being added to the newly synthesised strand of DNA which in the next round of replication can become a permanent mutation. During the 2nd round of replication, each of the daughter strands is replicated individually - 50% of the daughter cells end up with the mutation
What are the 3 ways a cell deals with an abasic site
repaired through base excision repair, tolerated (through recombination or translesion synthesis) or neither and induces apoptosis
repair - high fidelity
tolerated - can lead to mutation by adding wrong base
What can 8-oxoG pair with
it can follow normal Watson and Crick base pairing and pair with a C or it can follow Holstein base pairing and pair with an A
What proteins are involved in the repair of 8-oxoG
OGG1 and MUTYH
Role of OGG1
removes 8-oxoG to reform an abasic site which can then be repaired
What mechanism repairs the abasic site formed by OGG1
short patch excision repair
Role of MUTYH
can remove A that has been added to the new strand of DNA opposite the 8-oxoG site
short patch vs long patch base excision repair
short patch repairs 1 wrong base, long patch repairs 2-20 wrong bases
enzymes and proteins involved in short patch excision repair
APE1, DNA pol beta and DNA ligase
enzymes and proteins involved in long patch base excision repair
APE1, DNA pol beta, DNA ligase, Pol epsilon and delta + PCNA, FEN1
APE1
apurinic endonuclease 1 - makes ssDNA break between the abasic site and the base before it
mutation in MUTYH
results in 8-oxoG not being repaired therefore get G-C> A-T transversion in the next round of replication.
Mutation in MUTYH reduces affinity for OGG1 and so fewer 8-oxoGs are repaired
what stage of the cell cycle does short and long patch base excision repair occur
short patch can happen at all stages, and long patch can only happen during S phase i.e. during replication
why are SSB in DNA so bad
because they can lead to DSB
Causes of SSB
ROS, base excision repair, removal of rNTPs in DNA
Why are DSB in DNA so bad
because they lead to genome instability
causes of DSB
ssbreaks, external factors (e.g. radiation or oxidation)
Mechanisms to repair dsDNA breaks
NHEJ, HR, alternative-NHEJ, single-stranded annealing
