DS-DNA Repair

Question 1

Name three common ways that double-stranded DNA breaks occur.

Answer 1

1. Naturally
2. Damage from ionizing radiation
3. Medical tests and treatments

Question 2

How are double-stranded DNA breaks sensed?

Answer 2

Two PIKKs (phosphatidylinositol 3-kinase related kinases) sense double-stranded DNA breaks:
ATM (ataxia telangiectasia mutated)
ATR (ataxia telangiectasia RAD3 related)

Question 3

When is NHEJ (non-homologous end joining) used to repair double-stranded DNA breaks, and what are the advantages and disadvantages to this pathway?

Answer 3

NHEJ is used in response to ionizing radiation and for VDJ recombination in the immune system

Advantages: quick repair; anytime during the cell cycle; not sequence dependent

Disadvantages: fidelity is imperfect; lose a few nucleotides whenever performed

Question 4

When is HR (homologous recombination) used to repair double-stranded DNA breaks, and what are the relative advantages and disadvantages to this pathway?

Answer 4

HR occurs during and right after DNA replication in S and G2 phases

Advantages: no gain or loss of nucleotides when performed; repair breaks perfectly

Disadvantages (sorta): requires nearly identical DNA strands of unbroken sister chromatid; multiple step process