cycle 4 Flashcards
mechanism of proofreading
corrects errors made by DNA polymerase during replication
facilitated by DNA polymerase. as enzyme adds complementary nucleotides, simultaneously checks for errors in base pairing. if error found, DNA polymerase utilizes exonuclease activity to remove the mismatched nucleotide from the 3’ end
mechanism of mismatch repairs
corrects errors made during replication that escape proofreading
mismatch repair system scans newly formed DNA for any inaccuracies in the base pairing. if error detected, mismatch repair proteins excise incorrect nucleotide, and correct nucleotide is inserted
mechanism of excision repair
corrects various kinds of DNA damage, such as those cause by chemicals and radiation
specialized proteins recognize region of damaged DNA. damaged segment is excised or cut out by endonucleases. DNA polymerase synthesizes new strand. ligase seals gaps
when each mechanism is most likely to be used
proofreading - during DNA replication
mismatch repair - after DNA replication. is important in the prevention of cancer
excision repair - after exposure to environmental factors causing DNA damage (UV radiation, chemicals)
difference between DNA damage and mutation
mutation - double-stranded change in the base sequence of a region of DNA
damage - changes that affect only one strand of the double helix
types of DNA damage
exogenous, endogenous
exogenous damage
outside, from environment, damage DNA directly
UV light, chemicals (smoking, medication, air pollution)
ionizing radiation
endogenous damage
inside cell
metabolism (in mitochondria, electron transport chain - only place where electrons flow singularly. electrons bind with O2, ROS (reactive oxygen species) damages DNA)