DNA Repair/Recombination Flashcards
Disease caused by a defect in the DNA repair pathway, nucleotide-excision repair. Unable to repair DNA damage by UV light, causing skin cancer.
Xeroderma Pigmentosum
Three types of DNA repair involving excision and subsequent replacement
1) mismatch repair
2) nucleotide excision repair
3) base excision repair
What protein helps mediate correct sequence determination in mismatch repair?
Mut proteins
What causes Hereditary Nonpolyposis Colorectal Cancer (HNPCC), otherwise known as Lynch Syndrome?
Mutations in mismatch repair
UV light can cause adjacent pyrimidine bases to do what?
dimerize
Subtype of endonucleases used to repair pyrimidine dimers?
exinuclease
How does exinuclease differ from endo/exonucleases?
It cuts with two nicks, not one.
Two major reasons base-excision repair is needed
1) Spotaneous deamination of cytosine to uracil
2) deamination of adenine to hypoxanthine
What is the enzyme which recognizes and removes uracil at the start of base excision repair?
uracil glycosylase
For step 2 of base excision repair, what enzyme nicks the backbone of the damaged strand at the missing base (apyrimidinic site)?
AP endonuclease
For step 3 of base excision repair, which enzyme removes the base free phosphate residue
Deoxyribose phosphate lyase
Which DNA Polymerase fills the gap in base excision repair?
DNA Polymerase I
How does ricin act on DNA or RNA
Depurination of rRNA
What’s the problem if guanine is methylated to O6-Methylguanine?
It messes up its hydrogen bonding
Which DNA repair mechanism does not involve DNA polymerase?
Direct repair
What process is responsible for correcting pyrimidine dimers in bacteria?
Photoreactivation
In direct repair, what enzyme converts O6-methylguanine back into regular guanine
methyltransferase
What are the two mechanisms for double stranded break repair?
1) Nonhomologous end-joining repair (NHEJ)
2) Homologous recombination repair (HR)
What causes a need for double stranded break repair?
High-energy radiation and oxidative free radicals
Which of the two double stranded break repair is more error prone?
Nonhomologous end-joining repair
The BRCA1 and BRCA2 genes are involved in what process?
homologous recombination repair
How does homologous recombination repair work?
Uses the same machinery/enzymes as homologous recombination in meiosis. It’s availability depends on the stage of the cell cycle
DNA recombination in which it occurs at aligned points on the genetic map so that no information is lost.
Legitimate recombination
Fidelity of DNA is not preserved. Recombination occurs between DNA segments not aligned on the genetic maps.
Illegitimate recombination
Crossing over of homologous chromosomes, leading to the switching of genetic material between them.
Holliday junction
The movement of transposons from one site to another is an example of…
illegitimate recombination
What type of transposon is known to cause many human diseases?
the movement of Alu sequences
