DNA Repair Systems Flashcards
Two examples of enzymes involved in direct repair of damaged bases.
DNA photolyase and O6-alkylguanine alkyltransferase
Why is O6 alkylG mutagenic
It can mispair with T resulting in a GC –> AT transition
What are the three major types of DNA repair systems?
Direct repair of damaged bases, excision repair, and mismatch repair
What are the two types of Excision repair?
Nucleotide excision repair and base excision repair
What is the difference between DNA photolyase and UvrAB complex?
DNA photolyase is light activated, breaks the dimer, limited penetration into the skin.
UvrABcomplex requires ATP, makes endonucleolytic cuts to REMOVE nucleotides, and does not need to be light activated, and repairs other types of damage
Nucleotide excision repair: Identifies the site of damage
UvrAB complex
Nucleotide excision repair: exinuclease that makes endonucleatic cuts (5’ and 3’) to the lesion
UvrBC
Nucleotide excision repair: unwinds and removes the excised piece
Helicase
Nucleotide excision repair: Fills the resultant gap
DNA pol I
Nucleotide excision repair: seals the nick in the backbone
DNA ligase
Featured enzyme of Base Excision Repair
DNA-N-Glycosylases
How do DNA-N-Glycosylases work?
They specifically recognize incorrect bases in DNA and remove them by creating apurinic or apyrimidinic sites.
Base excision repair: A mismatched uracil is identified by_________ , which cleaves the base from the ____ _______ to create an _______ site.
Uracil-DNA glycosylase, DNA backbone, apyrimidinic site
Base excision repair: removes the sugar residue from the backbone. Where does this enzyme cleave the backbone relative to the site?
Endonuclease, 5’
Base excision repair: enzyme that removes the damaged region plus a few more nucleotides. What activity of this enzyme is used?
DNA Pol I, 5’ exonuclease activity
Base excision repair: fills the gap
DNA pol I
Base excision repair: closes the nick in the backbone
DNA ligase
Which repair systems require ATP?
Nucleotide excision repair and mismatch repair
Which repair system directly scans for methylated strand?
Mismatch repair
Carries out methyl-directed mismatch repair
MutHLS system
Mismatch repair: binds to DNA at the site of mismatch. Followed by two others called:
MutS; MutL and Mut H
Mismatch repair: using ATP hydrolysis for energy, it pulls DNA in from both directions until reaching a sequence on the template strand. What is this sequence?
Must S, GATC
Mismatch repair: cleaves the unmethylated DNA strand 5’ to the G in the GATC sequence that is mirrored in the new strand.
MutH endonuclease
Mismatch repair: unwinds the DNA back past the mismatch
DNA helicase II
