Term: nucleotide bases https://doi.org/10.1351/goldbook.N04254 Definition: The heterocyclic pyrimidine and purine compounds which are constituents of all nucleic acids. Adenine (A), guanine (G) and cytosine (C) are found in both DNA and RNA, thymine (T) is found (primarily) in DNA and uracil (U) only in RNA. Related Terms: 1) nucleic acids (http://doi.org/10.1351/goldbook.N04245). 2) dna (http://doi.org/10.1351/goldbook.D01597). 3) rna (http://doi.org/10.1351/goldbook.R05386). Source: PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 147 (https://doi.org/10.1351/pac199264010143) Citation: 'nucleotide bases' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.N04254 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.