Homologous recombination — Flashcards

Flashcard 1: Nonhomologous End Joining (NHEJ) occurs _____ S phase of the cell cycle

Answer: before (before/after?)

Flashcard 2: What phase of the cell cycle do nucleotide excision repairs occur?_____

Answer: G1

Flashcard 3: Is homologous recombination error prone?_____

Answer: No

Flashcard 4: Mechanisms to repair _____ breaks are defective in Ataxia telangiectasia, Fanconi anemia, and SCID

Answer: dsDNA

Flashcard 5: What form of DNA repair fixes mutations induced by UV radiation?_____

Answer: nucleotide excision repair

Flashcard 6: What are the four mechanisms of DNA repair?

Answer: Nucleotide excision repair Base excision repair Mismatch repair Nonhomologous end joining

Flashcard 7: non-homologous end joining

Answer: join 2 dsDNA ends

Extra: Used for double-stranded breaks when no homologous chromosome is available as a template. Clinical correlations: - Ataxia-telangiectasia (ATM gene defect in DNA break repair signaling) - SCID (Defects in NHEJ, e.g., DNA Ligase IV, Artemis)

Flashcard 8: mismatch repair

Answer: 1. new strand recognized (lacks methylation) 2. mismatched nucleotides removed 3. DNA pol/ligase fills/seals gap

Extra: Mismatched bases on newly synthesized DNA strandhereditary nonpolyposis colorectal cancer (HNPCC)

Flashcard 9: base excision repair (BER)

Answer: 1. specific glycosylases recognize and remove damaged bases 2. AP endonuclease removes AP DNA 3. DNA pol/ligase fill/seal gap

Extra: spontaneous/toxic changes to the base itself; most often deamination

Flashcard 10: nucleotide excision repair (NER)

Answer: 1. endonuclease removes short ssDNA segment containing lesion 2. DNA pol/ligase fill/seal gap

Extra: bulky adducts, commonly thymine dimers caused by UV radiation xeroderma pigmentosa