DNA Damage I

Question 1

Sources of DNA Damage

Answer 1

Normal Transcription
Environmental Agents (UV light, Chemical)
Internal Stress (ROS)

Question 2

Types of DNA Damage

Answer 2

modified/mismatched/missing nucleotides
double stranded breaks

Question 3

Direct Reversal

Answer 3

• no excision and error free
• transfer modifications to another source

Question 4

Mismatch Repair

Answer 4

• recognize by MUTS and MUTL
• MUTL = nick in DNA
• exonuclease removes mismatch + DNA Pol restore

Question 5

Base Excision Repair

Answer 5

• removed damaged nucleotide by glycosylase
• AP nuclease strand invasion
• DNA Pol add new nucleotide + ligation

Long BER
- Fen1 repair 5’ flap

Question 6

Nucleotide Excision Repair

Answer 6

• repairs distorted double helices
• transcription coupled vs global genome
• lesion detection
• local unwinding + damage verification
• excise DNA around lesion
• DNA synthesis + ligation

Question 7

Homologous Recombination

Answer 7

• DSB recognized by MRN complex (degrade 5’ ends)
• recruits ATM (pair with matching chromosome)
• BRCA1 complex forms (DNA synthesis)
• D loop forms –> resolve by cutting

Question 8

Non Homologous End Joining

Answer 8

• Ku70/80 + DNA-Pkcs + Artemis (trim DSB)
• end process + extension
• LigIV/XRCC4 = ligation

Question 9

HR vs NHEJ

Answer 9

HR
- less frequent, active in S/G2 phase, complete repair, need sister chromosome

NHEJ
- more frequent, active in G1, error prone, no homology