DNA repair review Deck

Question 1

what are the steps in base excision repair? (5)

Answer 1

• enzymes recognize error and “flip” base
• glycosylase removes base
• endonuclease removes sugar-phosphate
• DNA pol B fills in gap
• ligase rejoins strand

Question 2

when is base excision repair employed?

Answer 2

when one base is altered, like deamination

Question 3

what are the steps in nucleotide excision repair? (5)

Answer 3

• damage is recognized
• local unwinding of DNA
• 2 cuts for dual strand excision
• gap filled by DNA pol
• nick sealed with DNA ligase

Question 4

when is nucleotide excision employed?

Answer 4

when bulky lesions that lead to DNA distortion are present (like thyimine dimers)

Question 5

what is a nucleotide excision repair related disease?

Answer 5

xeroderma pigmentosa- high sensitivity to UV light, results from defect in one of the seven genes responsible for nucleotide excision repair

Question 6

what is the purpose of the mismatch repair system?

Answer 6

corrects mismatches of normal bases

Question 7

what enzymes are used in the mismatch repair system?

Answer 7

MSH2- recognizes mismatch

MLH1- cuts out mismatch

Question 8

what is a clinical application of the mismatch repair system?

Answer 8

inherited colon CA (HNPCC) secondary to inactivation of one or more mismatch repair genes

Question 9

how can the mismatch repair machinery differentiate between parental and daughter strands?

Answer 9

parents strand will be more heavily methylated

Question 10

what occurs in non-homologue end joining?

Answer 10

loss of nucleotides occurs due to degradation at both ends, free ends are forced together, yields mutation

Question 11

in what type of cells does NHEJ give an advantage?

Answer 11

cancer cells- gives survival advantage

Question 12

when does homologous repair occur?

Answer 12

S/G2

Question 13

in SSB repair, which enzymes:
detect break?
clean out area?
fill in bases?
seal nick?

Answer 13

detect break- PPAR 1/2
clean out area- TDP1/PNKP
fill in bases- DNA pol B
seal nick- DNA ligase III

Question 14

in DSB repair, which enzymes:
detect break?
clean out area?
fill in bases?
seal nick?

Answer 14

detect break- DNA PKcs+KU 70/80
clean out area- PNKP and artemis
fill in bases- DNA pol mu and lambda
seals nick- DNA ligase IV

Question 15

what is regulated by BRCA 1? BRCA 2?

Answer 15

BRCA1- NHEJ and homologous recombination

BRCA2- homologous recombination