DNA repair

DNA repair is the set of molecular tools a cell uses to find and fix damage and copying errors in its DNA, before those flaws become permanent mutations. Think of a vigilant proofreading and maintenance crew that patrols the genome around the clock, catching most mistakes the moment they appear.

Different kinds of damage call for different repair pathways. A single wrong base left after copying is corrected by mismatch repair; a chemically altered base is cut out and replaced by base or nucleotide excision repair; and breaks across both strands are mended by homologous recombination or by directly rejoining the ends. Each pathway uses dedicated enzymes that recognise a specific kind of lesion.

Repair is what keeps the mutation rate as low as it is; without it, errors would accumulate ruinously fast. When repair genes themselves are defective, mutations pile up across the genome, a condition called genomic instability that strongly predisposes to cancer. The importance of these mechanisms was recognised with a Nobel Prize in Chemistry in 2015.