DNA repair Flashcards
what are mutagens
chemical agents that disrupt the original DNA sequence
how do mutages alter DNA
oxidation
deamination
alkylation
UV rad
Xray exposure
was is oxidation
the interaction between a base and an oxygen radical.
This commonly happened with guanine to form8-Oxogunaine, an alter guanine base that pairs with adenine instead of cysteine.
what is deaminiation
the removal of an NH2 group off of adenine, cystine or guanine by hydrolysis. This commonly replaces the NH2 group with a carbonyl group. this won’t happen to thymine as there are no NH2 groups.
cystine deamination
removal the NH2 group and becomes uracil. NH2 group is replaced with a carbonyl unit
adenine deamination
removes NH2 group, changes it into a carbonyl group to which it will BP with cystine, not thymine
what is 5 methylcytosine and what happens when it is deaminated
an alkylated cytosine base commonly produced to regulate gene transcription. when deaminated, it will turn into thymine
what is alkyation
the addition of an alkyl group. either base will be added to a more complex unit or a simple alkane will be added to the base.
what dies UV light do?
forms pyrimidine dimers (form pyrimidine that is adjacent to one another) which cause a kink/ bludge in the DNA structure.
what are the steps for repair
recognize the damage
remove the damaged region
repair the region by filling with the correct nuc
what are the types of repair
mismatch
direct (DNA photolyase)
nucleotide excision repair
base excision repair
mismatch base repiar
uses a trio of MUT enzymes
MutS recognizes the issue and signals MutL. MutL binds to Mut S and signals for to MUT H yo come and internally cleave the section (with endonuc)
an exonuc follows and takes out the damaged part. DAN pol3 fills in the new bases
direct repair
does not remove any fragments
uses light energy to excite e- (to transfer to FADH) and cleave pyrimidine dimers via the use of DNA photolyase
nucleotide excision repair
can be completed in the dark
Uvr ABC is the excinuclease that sees a mismatch kink and will cleave the site surrounding the area
DNA pol 1 fills the gap, followed by ligase
base excision repair
a defective base won’t BP and will flop out (invert the phoso backbone. It will ultimately flip into a glycosylase.
AP is recruited and will clip the backbone
deoxyribose phosphodiesterase removes the clipped base unit
DNA pol 1 adds the new base
ligase seals the strand
note that this will only sove one incorrect base at a time
