Molecular Mechanisms of Radiation Effects

Abstract

Publisher Summary This chapter reviews the photochemistry of nucleic acids and discusses the difference in the reaction of thymine to ultraviolet (UV) irradiation in aqueous solution or frozen in ice. It demonstrates that thymine forms a dimer when UV irradiated in ice. If dimerization occurs within an individual DNA strand, the biological consequence may be an altered tendency to pair with the adenine of the complementary strand. The altered strength of the sugar-base linkage of deoxyribose in thymidine dimer is an indication of the changed electron density in the pyrimidine structure and this changes the ability to form hydrogen bonds. But if dimerization occurs between the two individual strands of DNA, the dividing mechanism of the cell may be completely blocked. Although an intermolecular dimerization in native DNA appears improbable, during cell duplication there are phases with cleaved DNA strands in which intermolecular dimerization is more likely. The model experiments show that both forms of dimerization are possible. The chapter describes that the different behaviors of bacteria under UV irradiation or X irradiation demonstrate that both kinds of radiation act fundamentally differently, although the point of attack in the cell is the same: the nucleic acids. The great specificity of UV radiation permitted the rapid discovery of the chemical basis of biological UV inactivation.