DNA Damage and Repair Flashcards
(11 cards)
what is the definition of a mutation
a heritable change in the sequence of the DNA at a cellular level, ie a change in the genotype
T/F damaged DNA is mutated DNA
False. Damaged DNA causes mutated DNA.
Describe mismatch repair
it corrects for incorrect bases incorporated during DNA replication by using the methylation differences in daughter and parent strands. In bacteria MutH binds to sequences only methylated on one side. MutS scans until it finds a mismatch. MutL links the two together. MutH cuts out the DNA in between, and DNA polymerase and ligase fill in the gap
what is the difference between direct and indirect carciongens
direct actively covalently modify DNA bases. indirect are inert until converted into carcinogens by the liver cytochrome p450 system
most, but not all, mutagenic substances are carcinogenic. all carcinogens are mutagens.
ok
describe nucleotide excision repair
NER repairs environmental damage. this damage causes a physical distortion in the DNA. A dimer of XPC and hHR23B senses the distortion. this dimer attracts TFIIH and XPG. TFIIH unwinds the helix via XPB and XPD. XPA and RPA stabilize the unwound helix. XPG makes a 3’ cut and ERCC1 and XPF make a 5’ cut. The gap is filled via DNA polymerase and ligase.
what are some causes of double strand DNA breaks?
chemotherapy. radiation. replication fork collapse.
what is the most damaging type of DNA mutation
double strand break b/c of the potential for gross loss of genetic material
Describe homologous recombination repair
an error-free process where a homologous strand is used as a template to repair double stranded DNA breaks. it requires a sister chromatid and thus can only occur in S or G2 phase. A protein recognizes the break, and removes a portion of the 5’ end of each strand to create an overhang. The DNA exchanges strands and the homolog acts as a template for the damaged strand
Describe nonhomologous end joining
an error-prone process for resolving double strand breaks. it involves ligating free double strands together with no specificity and is the dominant repair pathway in mammalian cells.
Describe the Ames test
create a bacteria incapable of producing His with no NER and expose it to a potential mutagen. If the colony begins producing His, it indicates a mutation occurs. To test for indirect acting mutagens, also add liver homogenate.
