DNA Repair

DNA is subject to spontaneous instability and decay. In addition to spontaneous damage, cellular DNA is under constant attack from reactive chemicals that the cell itself generates as by-products of metabolism. Moreover, the integrity of cellular DNA is assaulted by such environmental threats as X rays, ultraviolet radiation from the sun, and many chemical agents, some of which are products of our industrialized society.

Since mutations can be introduced into DNA as a consequence of DNA damage, there is currently great interest and concern about the expanding list of chemicals released into the environment. In humans, damage to DNA has been implicated in many cancers as well as in certain aspects of aging. Genetic diseases such as cystic fibrosis and sickle cell disease can be caused by a single DNA mutation in one gene.

Figure 1. Four types of mutation: (A) complete loss of a base. (B) Loss of an amino group, converting a cytosine to a thymine. (C) Addition of a small alkyl group, such as-CH3. (D) Reaction with oxygen.