9b. Indirect DNA repair systems 1 Flashcards
what is a feature of indirect DNA repair and name three types of categories
indirect DNA repair synthesises new DNA
- base excision repair
- nucleotide excision repair
- mismatch repair
what is generalised base excision repair?
the DNA base that is damaged/incorrect is removed
look at picture
what enzyme removes the base in generalised base excision repair? what does it leave the DNA strand with?
DNA glycolases remove the base.
the strand is left with an AP site
what repairs the gap in the DNA from having the base taken out?
DNA polymerase 1, then DNA ligase repairs the gap
what are two ways that uracil is incorporated into DNA?
- uracil is misincorporated into DNA by DNA pol 3
- from spontaneous deamination of cytosine
look at image to see how they are closely related to pyrimidines
how is it that DNA misincorporates uracil into DNA? (two points - think about bonding)
- uracil can make the same hydrogen bonds with adenine as thymine does
- DNA pol 3 cant deffirnatiate between dUTP and dTTP when base pairing
what is the result if uracil is misincorporated into DNA?
nothing happens because the uracil will be in the same place as the thymine, therefore during replication will not make a difference
how does spontaneuous deanimation of cytosine occur?
the cytosines amine group will go away and be replaced with a double bonded oxygen.
this means the cytosine is turned into a uracil while its sitting in place
what is the result of the spontaneous deanimation of the DNA strand when its replicated?
the uracil (which should be a cytosine) will template an adenine (which should be a guanine - to cytosine)
what enzyme removes uracil when there has been either of the two ways (spontaneous or misincorporates) of uracil into DNA?
Uracil-DNA-N-Glycosylase
this is a specific enzyme for removing uracil.
how does uracil-DNA-n-glycosylase remove uracil? (two steps)
its catalyses the N-glycosidic bond
leaves a free OH group
*its the same as base excition
what is the difference in misincorporates compared to a spontaneous reaction?
misincorporates: uracil is in place of a thymine (no worries)
sponatenous: deanimation causes cytosine to become uracil (problem)
why does the cell remove uracil from DNA?
the cell dosent know if it was misincorporation or sponaneous, therefore theres a risk of a potential mutation. this is removed
