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A compound consisting of three essential parts - a purine or pyrimidine base linked to carbon-1 of a pentose sugar (either ribose or deoxyribose), which in turn is esterified on carbon-5 to phosphoric acid. Polynucleotides are polymers of nucleotides. There are two types: RNA, which contains ribose, and the bases uracil, adenine, guanine, and cytosine; and DNA, which contains deoxyribose, and thymine, adenine, guanine, and cytosine. Both play an informational role in the cell. In contrast, dinucleotides, such as nicotinamide adenine dinucleotide (NAD) and flavin adenine dinucleotide (FAD), function as hydrogen carriers, while mononucleotides, such as adenosine triphosphate (ATP), serve as energy carriers.
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