9c. Indirect repair systems 2

Question 1

what is nucelotide excision repair? three factors of it

Answer 1

• a back up mechanisms
• when the DNA damage is bulky its used
• removes multiple nucleotides

Question 2

what are the four steps for the nucelotide excision repair to work?

Answer 2

1. damage recognition: excinuclease recognises the damage
2. nick: removes about 12 nucleotides
3. DNA polymerase: will synthesise new DNA
4. DNA Ligase: binds DNA back together

have a good look at picture

Question 3

what is mismatch repair?

Answer 3

• scans DNA and removes replication errors - a wrong base that escapes proof reading
• repairs damage

Question 4

what is the enzyme the recognised mismatched mutations?

Answer 4

MutHLS

(mut for mutation)

Question 5

mismatch repair: how can the enzyme tell which which strand carries the DNA?

Answer 5

DNA is methylated on every adenine on a GATC sequence (approx every 250 nucelotides)

this methylation allows the parental strand to be distinguished from the daughter replicated strand

Question 6

what are the steps of mismatch repair? 5 steps

Answer 6

Question 7

mismatch repair 1: what does MutS do when finding a mismatch

*two enzymes

Answer 7

it binds to the DNA strand and finds the mismatch, then recruits MutL and MutH

Question 8

mismatch 2: what does MutL and MutH do?

Answer 8

MutL locates the methylated adenine

MutH makes the nick on the new strand opposite the methylated

Question 9

what fills in the gap in the DNA?

Answer 9

DNA polymerase 3 fills in the DNA