PLoS Biology has published an introduction to DNA repair mechanisms and some of their implications. A portion of degenerative aging - not to mention cancer - is caused by a buildup of DNA damage. This is a problem that must be solved along the way to working healthy life extension medicine: "You probably weren't thinking about your body's DNA repair systems the last time you sat on the beach in the bright sunshine. Fortunately, however, while you were subjecting your DNA to the harmful effects of ultraviolet (UV) light, your cells were busy repairing the damage. The idea that our genetic material could be damaged by the sun was not appreciated in the early days of molecular biology ... it was assumed that DNA is fundamentally stable since it carries the blueprint of life. However, more than 50 years of research have revealed that our DNA is under constant assault by sunlight, oxygen, radiation, various chemicals, and even our own cellular processes."

Link: http://biology.plosjournals.org/perlserv/?request=get-document&doi=10%2E1371%2Fjournal%2Epbio%2E0040203