Biochemistry - The Chemical Reactions of Living Cells, Volume 1 - D. Metzler 1980

The Molecules We Are Made Of
Nucleic Acids
Chemical Reactions Involving Polynucleotides

Both DNA and RNA are readily hydrolyzed by acids (Section 3.2). The glycosidic bonds in DNA are more labile than those in RNA. Purine NUCLEOTIDES are hydrolyzed more easily than pyrimidine ones. Yet, despite the ease with which Nucleic Acids degrade under the action of acids and alkalis, the covalent backbone of these molecules is relatively stable, which underlies their ability to serve as genetic material. Nevertheless, both DNA and RNA participate in a multitude of Chemical Reactions.

Nitrous acid reacts with the amino groups of the bases, converting them into —OH groups. The resulting group

Class="center">

undergoes tautomerization and takes the form

Thus, upon interacting with nucleic acids, nitrous acid converts cytosine into uracil and, consequently, acts as a potent chemical mutagen (Chapter 15, Section 3.1). Similarly, adenine is converted into hypoxanthine, and guanine into xanthine. Another mutagenic compound, hydroxylamine (H₂N—OH), reacts with carbonyl groups (especially in Pyrimidines), even though these carbonyl groups are part of a cyclic amide Structure and therefore exhibit relatively low reactivity.

Pyrimidines are readily reduced by sodium borohydride NaBH₄ [equation (2-12)]. Uridine, thymidine, and (to a lesser extent) cytosine within nucleic acids undergo dimerization upon UV irradiation and are hydrogenated [equations (13-22) and (13-23)].

Formaldehyde reacts with the amino groups of purine and pyrimidine bases (Chapter 7, Section 3.3) [64].