Repair of DNA damage Flashcards
What is the direct reversal of DNA damage?
DNA polymerase proofreading activity: 3’ to 5’ direction
Base excision repair
Used by our cells to repair depurination and deamination
Describe base excision repair
Using a glycosylase enzyme to recognise and remove the damaged base. The bond between the base and the deoxyribose is cleaved by the glycosylase and other enzymes cleave the sugar-phosphate from the backbone, leaving a gap in the DNA sequence
State how nucleotide excision repair takes place in bacteria
- UvrAB scans and finds DNA damage
- UvrA’s released and UvrC binds
- The complex UvrBC cuts the DNA a bit in the 3’ and a bit in the 5’ direction
- UvrD binds and unwinds the regions between the cuts, releasing the damaged segment: DNA polymerase synthesises the single strand
How many Uvr genes are there in bacteria and mammals?
4 in bacteria
12 in mammalian cells
How do cells know which is strand is correct?
Using methylation
Ways a cell repairs a double-strand break
- Homologous recombination
- Non-homologous end-joining
Homologous recombination
Using the homologous chromosome to replicate the sequence in the other chromosome that has the double strand break
Describe the process of homologous recombination
When we have a double strand break, the break is degraded a bit at the ends. The strand has 2 gaps and we repair them through D looping where one strand invades the double strand of the homologous chromosome–> created a Holliday structure
Holliday structure
An arrangement in which the 2 strands of the homologous chromosomes are exchanged
Which genes act in the double-strand break repair of the cell?
BRCA1 and BRCA2
Non-homologous end joining
A double-strand break and we cannot repair it through homologous recombination
Why do we have loops at the end of telomeres?
Because otherwise the cell would recognise the end of telomere as a double-strand break
