Lecture 17 - Repair of DNA mutations Flashcards
What are the four different types of repair for mutations?
Direct repair
Excision repair
Mismatch repair
Nonhomologous end joining
What is the process of direct reapair?
- An enzyme corrects the change in a nucleotide caused by a mutagen
- Effects of alkylating agents can be repaired
- Base dimers formed by UV radiation can be directly repaired
What is the overall process of excision repair?
Damaged nucleotide is removed and the gap is filled by DNA synthesis
What are the two types of excision repair?
Base excision repair
Nucleotide excision repair
What is base excision repair?
One single altered base is removed
What is nucleotide excision repair?
A longer piece of DNA with altered bases is removed
How does base excision repair work in E.coli?
There is removal of the damaged base by a DNA glycosylase enzyme
The resulting AP site is filled in
How does nucleotide excision repair work in E.coli?
Done by the UvrABC endonuclease
The region containing damaged nucleotide is excised and resynthesised
What is mismatch repair?
Corrects errors in DNA replication
The parent strand contains the correct nucleotide and the daughter strand contains the mismatch
How is the mismatch distinguished in mismatch repair of E.coli?
EG in E.coli, the parent strand is methylated
The mismatch is recognised by the MutH and the MutS enzymes
The mismatch is excised and the DNA is resynthesised
How does mismatch repair work in humans?
Base-base mismatches are recognised by MutS like proteins
Another protein acts as an endonuclease
Human mismatch repair enzymes tightly associated with the replication fork, so they can recognise the daughter strand as its being synthesised
What is non homologous end joining?
It corrects DNA breaks
How are real breaks distinguished from natural ends of chromosomes in non homologous end joining?
Natural ends have telomeres to mark them
What is the process of non homologous end joining in humans?
There is a double strand break
Ku proteins attach to the end of each strand and attract one another
They join together
The DNA is repaired
