Lecture 10 Flashcards
What are 5 causes of double strand breaks?
Ionizing radiation, Alkylating agents, reactive oxygen species, torsional stress, and some enzymes
What is the most severe form of DNA damage?
Double strand breaks (DSBs)
What is an example of an Alkylating agent that can cause DSBs?
Cisplatin
What are the two types of double strand break repair?
Non-homologous end-joining (NHEJ) and homologous recombination (HR)
How does NHEJ work?
Broken ends are simply lighted back together
How does homologous repair work?
Any missing DNA bases are copied from homologous chromosome and the ends are lighted together
Which subpathway is the main repair pathway for DSBs generated by ionizing radiation?
NHEJ
When is HR most active?
During DNA replication
When is NHEJ most active?
G1/G0 phases of cell cycle
What is a Holiday Junction?
Junction between four strands of DNA
Where are Holliday Junctions found?
During homologous repair
During HR, what proteins bind the ends of the breaks and seek out the homologous chromosome?
RAD51 and BRCA-2
What are the three steps of homologous recombination?
Strand invasion, branch migration, and Holliday Junction
Ligation of ends during HR is accomplished by what enzyme?
DNA ligase 1
What is BRCA1’s role in homologous recombination?
Activates checkpoint
What complex is responsible for recognizing and binding DNA ends during NHEJ?
Ku70+Ku80
What are the three steps of eukaryotic mismatch repair?
- Recognition 2. Excision 3. Resynthesis
What protein complex is responsible for recognizing and binding mismatched bases?
MSH2:MSH6 complex (MutS)
What activities are present during excision?
Unwinding via helical and removal of base pairs via exonuclease
What protein fills the gap left by the DNA?
DNA polymerase D
What causes Lynch Syndrome?
Loss of function if MMR genes
What cancers are Lynch Syndrome associated with?
Colorectal cancers and endometrial cancers
What is a strong indicator of damaged/impaired mismatch repair function?
Microsatellite instability
What mutations does X-ray exposure cause?
Oxidized bases, ssDNA breaks, double strand breaks
What is PARP1 responsible for?
Single strand break repairs
What is BRCA2’s role in homologous recombination?
Stimulates recombination
