DNA damage is a structural lesion in the DNA molecule — the nucleotide order remains correct — and is formally distinct from a mutation, which is a change in the nucleotide sequence itself. Such lesions arise from exogenous agents (ionizing and ultraviolet radiation) and endogenous agents (chiefly reactive oxygen species generated as byproducts of the mitochondrial electron transport chain, which enzymes and antioxidants normally counteract); a canonical example is the pyrimidine dimer, a covalent linkage between two adjacent pyrimidine bases that distorts the sugar-phosphate backbone and disrupts complementary base pairing. Nucleotide excision repair resolves this lesion class through an ordered three-enzyme mechanism — endonuclease excision of the damaged segment, DNA polymerase resynthesis, and ligase sealing — and failure of such repair pathways leaves damaged cells to enter senescence, undergo apoptosis, or divide without regulation, the last constituting the basis of carcinogenesis. The topic belongs to molecular biology, specifically genome maintenance.
DNA damage is a structural lesion in the DNA molecule — the nucleotide order remains correct — and is formally distinct from a mutation, which is a change in the nucleotide sequence itself. Such lesi…