Chiolo Lecture 1 Flashcards
(30 cards)
What are examples of replication error damages?
Mismatches and Insertions/Deletions
What sources of DNA damage does mismatch repair solve?
- replication errors
- intercalating agents (EtBr)
How were DNA repair genes identified?
by their sensitivity of mutations to DNA damaging agents
What are “UVr” genes?
genes for nucleotide excision repair - loss leads to UV sensitivity
What are “Rad” genes?
genes for double-stranded break repair - loss leads to radiation sensitivty
What are “Mut” genes?
genes for mismatch repair - loss results in high mutation rate
What is one health issue that results from mismatch repair mutation?
hereditary non-polyposis colorectal cancer (HNPCC)
When do mismatches frequently occur?
during DNA replication
When are mismatches permanent?
they are not repaired before a new round of replication
What is the first protection against mismatches?
the proofreading activity of DNA polymerase
What is the function of DNA polymerase?
contains a 3’-5’ exonuclease domain that facilitates the removal of mismatched nucleotides
DNA polymerases raise the accuracy to:
10^-7 errors/bp
Mismatch repair raises the accuracy to:
10^-9 errors/bp
What components are needed for mismatch repair?
- parental strand (template)
- MutS
- MutL
- MutH
What is the function of endo-nuclease?
(‘nickase’) = cleaves the DNA bonds within the DNA molecule
What is the function of exo-nuclease?
cleaves the nucleotides at the end of a DNA molecule, require free 3’ or 5’ -OH, works with a helicase
Which Mut recognizes the mismatch as a “distorsion” in the DNA molecule?
MutS, recognizes a kink at mismatch
How is the parental strand recognized by Mut H?
by DNA methylation
What is the function of MutH?
binds the nearest methylated sites and cuts only non-methylated DNA
What is the function of Dam methylase?
adds methyl groups at 5’ -GATC sites (works before and after replication [before replication, Dam methylase methylates the parental strand. during replication, no methylation occurs. after methylation, Dam methylase methylates the replicate strand]) mismatch repair occurs before the methylation of newly synthesized DNA
What exonuclease is used in the 5’-3’ position?
Exo VII or RecJ
What exonuclease is used in the 3’-5’ position?
Exo VI
What is the function of MutS?
recognizes the mismatch
Does the nascent strand in eukaryotes need endonuclease?
No, no need for an endonuclease on lagging strand because Okazaki fragments
