35 - DNA repair and recombination

Proofreading of polymerase increases replication accuracy by ________ fold

1000

What is the first line of defense against DNA replication errors?

3’ to 5’ exonuclease proofreading activity

In mismatch repair, what senses the mismatched base?

MutS

What happens in mismatch repair?

A mismatched base is sensed by MutS, MutH cuts a nick into the DNA strand, and exonuclease 1 removes the region, allowing DNA polymerase to resynthesize the region, ligase fills in the last gap

Which form of DNA repair doesn’t require the removal of synthesized DNA? Do eukaryotes or prokaryotes have it?

Direct repair, only prokaryotes

Nucleotide excision repair: What specific nucleotides does it repair and how?

Only repairs pyrimidine dimers, damage is recognized, UvrABC excinuclease removes 12 nucleotides, DNA pol I synthesizes the strand, and DNA ligase joins it together

Xeroderma pigemtosum is a genetic disorder involving __________ genes

DNA nucleotide excision repair

What do xeroderma pigmentosum patients experience as a result of the disorder?

Extreme sensitivity to sun and much higher risk of skin cancer

Base excision repair

Modified base flips out, and glycosylase removes the SINGLE base, then AP endonuclease nicks the backbone allowing DNA polymerase I to resynthesize and ligase to fill in the backbone gap

Nucleotide excision vs base excision repair

Nucleotide excision involves UvrABC/nucleotide excision repair enzymes and excises 12 bases, base excision only cuts one base out and involves glycosylase and AP endonuclease instead

How do double stranded breaks in DNA occur?

Double stranded breaks result from ionizing radiation (like from the sun) or collapse of the replication fork

Can recombination fix damaged DNA?

Yes

Which protein is important in recombination to repair double stranded DNA breaks?

Rad 51

Ames test

Salmonella that can’t synthesize histidine were treated with mutagens, chemical caused histidine synthesis to be restored