Covalent backbone, of DNA

FIGURE 8-7 Phosphodiester linkages in the covalent backbone of DNA and RNA. The phosphodiester bonds (one of which is shaded in the DNA) link successive nucleotide units. The backbone of alternating pentose and phosphate groups in both types of nucleic acid is highly polar. The 5 end of the macromolecule lacks a nucleotide at the 5 position, and the 3 end lacks a nucleotide at the 3 position. 

The covalent backbone of DNA and RNA is subject to slow, nonenzymatic hydrolysis of the phosphodiester bonds. In the test tube, RNA is hydrolyzed rapidly under alkaline conditions, but DNA is not the 2 -hydroxyl groups in RNA (absent in DNA) are directly involved in the process. Cyclic 2, 3 -monophosphate nucleotides are the first products of the action of alkali on RNA and are rapidly hydrolyzed further to yield a mixture of 2 -and 3 -nucleoside monophosphates (Fig. 8-8). 

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