DNA Repair, and Homologous Recombination Flashcards
how does DNA polymerase proofread?
if the wrong nucleotide is added the DNA polymerase cannot grip it tightly
What is exonuclease activity
DNA polymerase senses a disruption (by not being able to tightly bind) and removes the incorrect base
what recognizes the mismatched bases in prokaryotic DNA?
MutS
What proteins are recruited to break the backbone of prokaryotes?
MutL and MutH
what does exonuclease do in prokaryotes?
removes successive nucleotides including ones with mismatched bases
What fills the mismatched DNA gap and binds it back together in prokaryotes?
DNA polymerase and DNA ligase
Describe the Strand-directed mismatch repair in eukaryotes.
- there is a error detected by the proofreading proteins
- DNA scanning by MutS and MutL detects a nick in the strand
- the entire strand hairpins and is removed
- exonuclease removes the successive nucleotides
- DNA polymerase fills the gap ligase joins the backbone
What are the most common types of DNA damage?
- depurination
- depyrimadination
- cytosine deaminiation
Where does oxidative damage generally occur?
Attacks carbon-carbon bonds
where do hydrolytic attacks occur?
bonds between carbons and nitrogens and on phosphorous atoms
where does methylation occur?
these only attack the nitrogen atoms
what is the most common outcome of deamination?
cytosine to uracil
what is a thymine dimer?
this is a covalent linkage between two neighbouring pyrimadine bases and occurs when DNA is exposed to UV radiation
what does Uracil DNA glycosylase do?
removes deaminated cytosine, fixes an added uracil
what does AP endonuclease do?
recognizes a deoxyribose sugar with a missing base, also fixes depurinations
Describe nucleotide excision repair:
- multi-enzyme complex recognizes a lesion
- a cut is made on each side of the lesion and a helicase removes the entire portion of the damaged strand
- DNA polymerase and DNA ligase fills in the missing DNA
- repair is coupled to transcription
What is the DNA damage contingency?
the polymerase stalls at DNA damage and a less accurate translesion polymerase specific to that type of damage comes in and reads through the damage and a replicative polymerase returns to fix it
What is better homologous recombination or nonhomologous recombination?
homologous recombination with sticky ends
