ABSTRACT
In Chapter 2 it was shown that components of cellular DNA could be damaged by ionizing radiation as a result of the action of hydroxyl free radicals generated from cell and tissue water molecules. It is now clear, however, that certain types of free radical, and related species, are actually generated quite normally in highly significant amounts by plant and animal cells. The aim of this chapter is to illustrate the oxidative damage that may occur in DNA as a result of cellularly generated free radicals. Although aerobic organisms gain a significant energetic advantage using molecular oxygen as the terminal oxidant in respiration, oxygen has the potential to be partially reduced in metabolic processes to yield reactive oxygen species (ROS). These include singlet oxygen, superoxide radicals, hydrogen peroxide and hydroxyl radicals. Although some serve vital cellular functions, for instance in immunological protection, they are potentially hazardous in that they may contribute directly or indirectly to a low background level of oxidative damage to cellular macromolecules, including DNA.
