(n´klētīd´´, ny´—)
, organic substance that serves as a monomer in forming nucleic acids. Nucleotides consist of either a purine or a pyrimidine base, a ribose or deoxyribose, and a phosphate group. Adenosine triphosphate serves as the principle energy carrier for the cell's reactions. The most important nucleotides are those derived from the bases adenine, guanine, cytosine, thymine, and uracil.