Solvents in pesticides, combustion smoke, viruses, ultraviolet radiation, and ionizing radiation can all damage the DNA of the cell. When DNA is affected by radiation, the greatest amount of damage is done to cell functions. The effect of ionizing radiation on a cell may be direct, or indirect (as when the radiation gets into the water that bathes the cells). Ionized free radicals damage the DNA molecules in cells. The DNA may undergo single-strand breaks, destruction of bases, and modification of the bases.
Even though DNA damage occurs frequently, there exist many repair mechanisms in the cell. These repair mechanisms include p53 and the re-synthesis of the DNA. p53 is a gene which encodes a protein that regulates the cell cycle. The protein encoded by p53 regulates the cell cycle and functions as a tumor suppressor. Most of the time, repair systems in the DNA work, but sometimes errors in the genetic code persist. Thus, these damaged cells have mutated. The mutated cell can be identified and eliminated by the immune system. However, a reduction in a large amount of normal cells or the production of a large amount of cancer cells can harm a human being. An increase in cancer cells may produce an increase in predisposition to a particular type of cancer; but it doesn’t guarantee that the individual will get cancer. Acquiring secondary cancer remains a risk of existing cancer patients treated with radiation therapy. Damaging results of radiation exposure may not present themselves for up to a decade.