lec 6. DNA repair Flashcards
factors that can cause DNA damage
- heat or water
- metabolic byproducts
- environment
- radiation
purines
double ringed nucleotides: adenine and guanine
pyrimidines
single ringed nucleotides: thymine (uracil in RNA) and cytosine
deamination
hydrolytic attack removes NH2 from cytosine converting it to uracil, so it now binds to adenine
depurination
the removal of a complete base due to oxidative damage, causing a frameshift mutation which makes missense proteins
pyrimidine dimers
UV light (photolytic conversion) causes a double bond between cytosine and thymine which distorts the DNA backbone and does not allow replication past that point
DNA breaks
double strand breaks caused by radiation, replication errors, and oxygen radicals which are particularly hazardous as there is no template strand for repair
Non-homologous end joining (NHEJ)
G1 - ends of DNA are stuck back together however there is a deletion of some DNA and no template specificity which can create frameshift mutations in a coding gene
Homologous Recombination
G2 - DNA gets processing done by nuclease. DNA uses template of homologous chromosome to restore structure. can get very accurate restoration.
Base Excision Repair (BER)
Repairs deamination with glycosylases which sample DNA and remove damaged bases. Then endonucleases and phosphodiesterase cut the backbone and take it out so DNA polymerase can fill it in with the correct base
Nucleotide Excision Repair (NER)
repairs prymidine dimers with excision nuclease which cuts 12 base pair ssDNA around the dimer. Then helicase, polymerase, and ligase put in new bases
trans-lesional DNA polymerase
substitutes for DNA polymerase when it encounters damaged DNA during replication. It lacks precision in template recognition and substrate base choice, and causes most base substitutions and single nucleotide deletion mutations
