Since it is impossible to preserve DNA from damage, it is necessary that as much damage as possible be reversed through repair. DNA is the only biomolecule that is specifically repaired. DNA repair is coupled to other highly important cellular processes. Cellular division will not proceed until damaged DNA has been repaired, and will not occur at all should the damage be too great. Strand-preferential repair is signaled during transcription.
Recombination can occur during repair.
In more complex organisms, DNA damage, including damage to the genes responsible for DNA repair themselves, can lead to tumor formation. The greater the amount of DNA damage incurred, the greater the risk that such damage may promote cancer. It is believed that many, perhaps most, cancers are at least partially attributable to defects in DNA repair. Sources of DNA Damage Before examining the different types of DNA repair, it is important to look at the sources of damage to DNA, as the source and type of the damage is the primary determinant of which type of repair mechanism is employed. Base loss Under normal cellular conditions, the glycosyl bond linking DNA bases with deoxyribose is slightly unstable.