DNA Oxidation and Repair Flashcards
What are the hotspots for mutation in DNA?
How is damage predominantly caused?
Groups exposed on replication.
DNA is negatively charged so metal cations bind and Fenton R proceeds in presence of H2O2. (Cu favourably binds GC-rich sequences).
Outline the comet assay.
DNA moves towards anode as negatively charged.
Presence of breaks in strand causes relaxation of supercoiled structure –> moves more quickly towards anode to form tail.
Fraction of DNA in tail reflects frequency of breaks.
How can proteins damage DNA?
Protein radicals can cross link with DNA base radicals. If they meet in chromatin –> DNA-protein cross-links interfere with chromatin unfolding.
What is BER used for?
One strand lesions mildly affecting base pairing.
8-oxoG, FAPyG or FAPyA
alkylated bases
Hypoxanthine
Uracil (from deamination of 5-methylcytosine.)
What is PRR?
Post replication repair.
Lesions encountered by DNA polymerase are resolved by translesion synthesis or error-free template switch combined with recombination.
What determines choice between the subpathways of PRR?
Modifications of PCNA
Monoubiquitylation of PCNA –> low fidelity polymerases that bypass lesions.
Polyubiquitylation of PCNA –> error-free pathways - less well understood.
How do cigarette smoke and H2O2 exposure differ in terms of the products formed on human bronchial epithelial cells?
Spencer et al 1996
H2O2 - increases in FAPy-A, FAPy-G and hydroxylated bases.
Cigarette smoke - hypoxanthine and xanthine in addition to above.
What products result from oxidation of cytosine, methylcytosine?
What products result from deamination of cytosine, 5-methylcytosine?
5-OHuracil or 5-OHhydantoin / after oxidation, rapid deamination to thymine glycol.
Uracil / Thymine
What products result from oxidation of thymine?
Thymine glycol if OH addition
OR H abstraction from methyl group –> 5-OH,Me-Uracil.
