DNA Repair LO Flashcards
Why is DNA the only macromolocule that is repaired?
RNA and proteins can be easily replaced but DNA cannot be replaced
what is a mutation?
permanent alteration of base sequences in daughter DNA
what are the positives of DNA mutations?
responsible for evolution, allelic variations, and polymorphisms in populations that makes us unique
what are the negatives of DNA mutations?
cancer and many human diseases
what are the 2 ways change-causing mutations can occur?
- uncorrected errors made during DNA replication
2. damage (oxidative, cleavage of DNA strand by radiation and chemicals, alkylation, depurianation, deamination etc)
what does deamination of C yield?
U
what are the 3 types of mutations?
point mutations
insertions
deletions
what is a point mutation?
substitution of one base for another
what is an insertion?
addition of one or more nucleotides within a DNA sequence
what is a deletion?
removal of one or more nucleotides from a DNA sequence
what are 2 examples of direct reversal of DNA damage?
- ligation of a break in phosphodiester backbone of DNA by DNA ligase
- repair of O6-methylguanosine by O6-methylguanosine methyltransferase (MGMT)
what is excision repair?
excision of a damaged region followed by precise replacement
what are the 3 types of excision repair?
- nucleotide excision repair (NER)
- base excision repair (BER)
- mismatch repair (MMR)
when is nucleotide excision repair (NER) used?
lesions that distort DNA structure and block RNA or DNA polymerase movement
how are thymine dimers formed and which process removes them?
UV radiation, removed by NER
what are the 2 ways lesions are recognized in NER?
- global genome NER
2. transcription-coupled NER
how does global genome NER work?
proteins recognize distoring DNA lesions in any region of the genome
how does transcription-coupled NER work?
recognized distorting DNA lesions in regions that are actively transcribed
what is the process of NER?
- recognition of damaged site by multi-protein complex
- local unwinding of DNA duplex by helicases (bubble of 25 bases)
- double incision of damaged strand by two endonucleases (about 30 bp)
- fill gap by DNA polymerase
- rejoin ends by DNA ligase