DNA repair is a collection of processes by which a
cell identifies and corrects damage to the
DNA molecules that encode its
genome. In human cells, both normal
metabolic activities and environmental factors such as
UV light and
radiation can cause DNA damage, resulting in as many as 1
million individual
molecular lesions per cell per day. Many of these lesions cause structural damage to the DNA molecule and can alter or eliminate the cell's ability to
transcribe the
gene that the affected DNA encodes. Other lesions induce potentially harmful
mutations in the cell's genome, which affect the survival of its daughter cells after it undergoes
mitosis. As a consequence, the DNA repair process is constantly active as it responds to damage in the DNA structure. When normal repair processes fail, and when cellular
apoptosis does not occur, irreparable DNA damage may occur, including double-strand breaks and DNA crosslinkages (interstrand crosslinks or ICLs).