Term: restriction enzymes https://doi.org/10.1351/goldbook.R05350 Definition: Endonucleases which recognize specific base sequences within a DNA helix, creating a double-strand break of DNA. Type I restriction enzymes bind to these recognition sites but subsequently cut the DNA at different sites. Type II restriction enzymes both bind and cut within their recognition or target sites. Related Terms: 1) dna (http://doi.org/10.1351/goldbook.D01597). 2) recognition sites (http://doi.org/10.1351/goldbook.R05199). 3) helix (http://doi.org/10.1351/goldbook.H02769). 4) enzymes (http://doi.org/10.1351/goldbook.E02159). Source: PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 164 (https://doi.org/10.1351/pac199264010143) Citation: 'restriction enzymes' 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.R05350 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.