Molecular Biology Lecture 9 - DNA Repair Flashcards Preview

Molecular Biology > Molecular Biology Lecture 9 - DNA Repair > Flashcards

Flashcards in Molecular Biology Lecture 9 - DNA Repair Deck (15):
1

DNA repair - E. coli

1. Direct reversal of DNA damage (pyrimidine dimers)

2. Mismatch repair

3. Excision repair
- base excision repair
- nucleotide excision repair
- transcription-coupled nucleotide excision repair

4. Recombinational repair (double-strand break repair)

5. Translesion polymerase

2

Direct reversal of DNA damage

1. UV light causes thymine dimers
2. Photolyase, activated by violet/blue light, reverses the reaction

2

Another Direct reversal of DNA damage

Methyltransferase removes methyl group from O6-methylguanine

3

Mismatch repair

1. MutS recognizes mismatch distortion

2. Recruits rest of the complex

3. SS endonclease followed by exonuclease

4. DNA pol III and DNA ligase


4

How does repair complex tell the mutant nucleotide from the correct nucleotide?

dam gene (DNA adenine methylase)
- methylates A in GATC
- Fig 9-5 is incorrect
- daughter strand is initially not methylated
Unmethylated daugher strand is repaired.

Must occur before daughter strand is methylated.
- MutH recognizes unmethylated GATC

5

Base-excision repair

1. For situations in which base has been changed or base analog has been inserted.

2. Specific glycosylase removes abnormal base (e.g. uracil, inosine, 8-oxoG.)
- specific glycosylase for each abnormal base

3. Abasic (apurinic or apyrimidinic) ribose is removed by nuclease.

4. DNA polymerase and DNA ligase repair gap.

6

Base-excision repair

1. What if DNA replication puts an A across form 8-oxoG?
2. Specific glycosylase removes the A.
3. Abasic site repaired to C.
4. 8-oxoG still present.

7

Base-excision repair

1. What if DNA replication puts an A across form 8-oxoG?
2. Specific glycosylase removes the A.
3. Abasic site repaired to C.
4. 8-oxoG still present.

8

Nucleotide-excision repair

1. Recognizes large distortion in DNA (modified base, thymine dimer)
2. Repair protein recognizes distortion.
3. DNA is locally denatured.
4. Endonuclease cuts DNA on both sides of the distortion
5. Gap is repaired by DNA polymerase and DNA ligase

9

Nucleotide-excision repair

1. Important in repairing UV damage in humans.
2. Xeroderma pigmentosum
- extreme sun-induced freckling, skin damage, skin cancer
3. Mutations in one of seven genes involved in either excision- repair or transcription-coupled excision repair pathway.

10

Transcription-coupled nucleotide-excision repair

1. Transcription is stopped or slowed by large distortions (e.g. thymine dimers).
2. One way of recognizing mutations.
3. Excision repair proteins are recruited and lesion is repaired.

11

DNA repair

1. Direct reversal of DNA damage
2. Mismatch repair

3. Excision repair
- base excision repair
- nucleotide excision repair
- transcription-coupled nucleotide excision repair

4. Recombinational repair (double-strand break repair)

5. Non-homologous end joining

6. Translesion polymerase

12

Double-strand break (DSB) repair

1. Many repair mechanisms rely on copying information from a wild-type sequence.
- mismatch and excision repair: copies template strand
- DSB repair
- both strands are damaged
- copies sister chromatid
- S and G2 in eukaryotes
- homologous chromosomes are not often used as repair templates
- DSB repair uncommon in G1

2. DSB repair is integral part of homologous recombination

12

DNA repair

1. Direct reversal of DNA damage
2. Mismatch repair

3. Excision repair
- base excision repair
- nucleotide excision repair
- transcription-coupled nucleotide excision repair

4. Recombinational repair (double-strand break repair)

5. Non-homologous end joining

6. Translesion polymerase

13

Double-strand break (DSB) repair

1. Many repair mechanisms rely on copying information from a wild-type sequence.
- mismatch and excision repair: copies template strand
- DSB repair
- both strands are damaged
- copies sister chromatid
- S and G2 in eukaryotes
- homologous chromosomes are not often used as repair templates
- DSB repair uncommon in G1

2. DSB repair is integral part of homologous recombination