| nitrogen base One of the nitrogen-containing purines (adenine or guanine) or pyrimidines (cytosine, thymine, or uracil) found in the nucleic acids DNA and RNA. The bases may be attached to a sugar (deoxyribose in DNA, ribose in RNA) to form nucleosides.The addition of a phosphate to a nucleoside results in the formation of a nucleotide, which is the basic constituent of nucleic acids. |