Practice question

Non-homologous end joining ligates broken chromosome ends without requiring homologous donor template, acting throughout cell cycle especially G1. Core factors Ku70/Ku80 anchor DNA ends, DNA-PKcs protects, Artemis trims, polymerases mu/lambda add nucleotides, and Lig4-XRCC4 seals ligation. Since processing removes or adds bases before joining, small insertions or deletions often arise at junction, causing frameshifts and mutations. This error-prone nature distinguishes it from homologous recombination which copies intact template accurately, but affords rapid survival when sister chromatid unavailable, critical for V(D)J recombination and class switching.