One of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base (one of four chemicals: adenine, thymine, guanine, and cytosine) plus a molecule of sugar and one of phosphoric acid.

Dr. Robert Nussbaum, of the National Human Genome Research Institute's Laboratory of Genetic Disease Research, defines nucleotide.

Related terms: base pair, deoxyribonucleic acid (DNA), genetic code (ATGC), ribonucleic acid (RNA).