Topic overview

Start with the big picture

Repair pathways differ in the lesions they recognize and how they restore DNA. Polymerase proofreading corrects many errors during replication, while mismatch repair addresses mispaired bases after synthesis. Nucleotide excision repair removes bulky, helix-distorting damage; base excision repair handles small, single-base lesions; and direct reversal repairs certain lesions without cutting the DNA backbone. Double-strand breaks can be repaired through homologous recombination or nonhomologous end joining, with alternative end joining serving as a mutagenic backup. When lesions remain, translesion synthesis can allow replication to continue at reduced fidelity. The lesson also introduces the bacterial SOS response and DNA damage signaling checkpoints, helping connect repair mechanisms to cell-cycle control and disease associations.