Although our cells are well equipped to handle small genetic insults from radiation, says Dr. Doetsch, problems arise when cells are subjected to either single large doses or years of cumulative exposure, or when key repair enzymes are missing or defective. DNA repair is a multi-step pathway designed to return damaged DNA back to its normal pristine state. Although there are several different types of DNA repair, Dr. Doetsch's interest is in base excision repair, accomplished by a team of repair enzymes, each assigned a different piece of the job. Finally, the strand is sealed back together. The initial steps of recognition and cutting are performed by specialized enzymes which deal only with specific types of genetic damage.
Some teams repair chemical damage, while others work with radiation damage.
Still others address the daily damage caused by oxygen free radicals that is the result of normal cellular function. Each type of damaging agent has its own unique effect on DNA, says Dr. Doetsch. Chemical carcinogens enter the cell's nucleus, bond with a component of DNA, and cause bulky formations that hang from the DNA strand. Nonionizing radiation, such as ultraviolet light, damages DNA through a photochemical process. Dr. Paul Doetsch specializes in DNA repair enzymes, which work to reverse many different types of genetic damage to the cell.