Chemical Changes Induced in DNA by Ionizing Radiation

Abstract

Publisher Summary This chapter discusses the effects of ionizing radiation on DNA. It focuses on the effects produced by irradiation in the presence of oxygen. The radiations whose effects are covered in the chapter—X rays, γ rays, and high energy electrons—interact with matter by transferring energy to the electrons in the irradiated sample. Usually, radiation effects on particular molecules, such as DNA, are ascribed to the sum of two processes: direct action and indirect action. By direct action, the effects of energy are deposited directly in the target molecule. By indirect action, the effects of reactive species are formed in the surroundings that diffuse to the target molecule and react with it. For DNA in dilute aqueous solution, the effects of irradiation are caused by the products formed by the action of ionizing radiations on water: the OH radical, the hydrated electron, the H atom, H2O2, and H2. OH radicals are the only reactive species in oxygenated solutions that react with any efficiency with the sugar. H atoms attached to each of the five carbon atoms can be extracted by OH. In oxygenated solution, oxygen reacts rapidly and irreversibly with each of the carbon radicals so formed. Extraction of an H atom from the 4´-C or the 5´-C of the sugar, then addition of O2, leads to strand breaks. H atom extraction from the 3'-C leads to unknown products. Extraction from C-1´ or C´-2 leads to alkali-labile bonds, which differ from the AP (apurinic or apyrimidinic) site formed by the depurination of DNA.