Our cells must have the ability to repair errors in their DNA to survive. If the DNA of dividing cells is sufficiently damaged, the DNA cannot be properly copied, and the cells cannot divide. Instead, they can age and die.

In both dividing and non-dividing cells, DNA is vital to their everyday functioning. The code in DNA is read by special enzymes and "translated" into the proteins that carry out all of our cellular and other bodily processes. Even small DNA errors can have serious effects. A single unrecognized and uncorrected DNA error can disable a critically needed protein and over time, result in disease or even death. DNA repair processes act by finding DNA damage and correcting it before too much of the damage is reproduced and accumulates. Some researchers contend that without DNA repair processes our cells would sustain enough damage to become useless within one year.

The genes in the nuclei of our cells are not the only sources of DNA in our cells. Cells also contain many tiny organelles called mitochondria. Mitochondria act as powerhouses for our cells, transforming oxygen and other fuels into the energy we need to live. Mitochondria possess their own DNA, and they use it to produce the proteins that carry out energy production. Because mitochondria use oxygen in energy production, their DNA is surrounded by free radicals (the toxic byproducts of energy production), and this greatly increases the amount of damage their DNA can sustain. For many years, scientists believed that mitochondrial DNA had no effective repair mechanisms. More recent research has shown that some mitochondrial DNA repair systems do in fact exist, but they are much less effective than those in the nuclei.⁶