DNA Repair Systems

Question 1

Two examples of enzymes involved in direct repair of damaged bases.

Answer 1

DNA photolyase and O6-alkylguanine alkyltransferase

Question 2

Why is O6 alkylG mutagenic

Answer 2

It can mispair with T resulting in a GC –> AT transition

Question 3

What are the three major types of DNA repair systems?

Answer 3

Direct repair of damaged bases, excision repair, and mismatch repair

Question 4

What are the two types of Excision repair?

Answer 4

Nucleotide excision repair and base excision repair

Question 5

What is the difference between DNA photolyase and UvrAB complex?

Answer 5

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

Question 6

Nucleotide excision repair: Identifies the site of damage

Answer 6

UvrAB complex

Question 7

Nucleotide excision repair: exinuclease that makes endonucleatic cuts (5’ and 3’) to the lesion

Answer 7

UvrBC

Question 8

Nucleotide excision repair: unwinds and removes the excised piece

Answer 8

Helicase

Question 9

Nucleotide excision repair: Fills the resultant gap

Answer 9

DNA pol I

Question 10

Nucleotide excision repair: seals the nick in the backbone

Answer 10

DNA ligase

Question 11

Featured enzyme of Base Excision Repair

Answer 11

DNA-N-Glycosylases

Question 12

How do DNA-N-Glycosylases work?

Answer 12

They specifically recognize incorrect bases in DNA and remove them by creating apurinic or apyrimidinic sites.

Question 13

Base excision repair: A mismatched uracil is identified by_________ , which cleaves the base from the ____ _______ to create an _______ site.

Answer 13

Uracil-DNA glycosylase, DNA backbone, apyrimidinic site

Question 14

Base excision repair: removes the sugar residue from the backbone. Where does this enzyme cleave the backbone relative to the site?

Answer 14

Endonuclease, 5’

Question 15

Base excision repair: enzyme that removes the damaged region plus a few more nucleotides. What activity of this enzyme is used?

Answer 15

DNA Pol I, 5’ exonuclease activity

Question 16

Base excision repair: fills the gap

Answer 16

DNA pol I

Question 17

Base excision repair: closes the nick in the backbone

Answer 17

DNA ligase

Question 18

Which repair systems require ATP?

Answer 18

Nucleotide excision repair and mismatch repair

Question 19

Which repair system directly scans for methylated strand?

Answer 19

Mismatch repair

Question 20

Carries out methyl-directed mismatch repair

Answer 20

MutHLS system

Question 21

Mismatch repair: binds to DNA at the site of mismatch. Followed by two others called:

Answer 21

MutS; MutL and Mut H

Question 22

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?

Answer 22

Must S, GATC

Question 23

Mismatch repair: cleaves the unmethylated DNA strand 5’ to the G in the GATC sequence that is mirrored in the new strand.

Answer 23

MutH endonuclease

Question 24

Mismatch repair: unwinds the DNA back past the mismatch

Answer 24

DNA helicase II

Question 25

Mismatch repair: removes the damaged DNA

Answer 25

exonuclease

Question 26

Mismatch repair: Fills the gap

Answer 26

DNA pol III

Question 27

Mismatch repair: seals the nick

Answer 27

DNA ligase