Science, Tech, Math › Science Nucleotide Definition in Chemistry What Is a Nucleotide? Share Flipboard Email Print Getty Images / KTSDesign Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 03, 2019 Nucleotide Definition: A nucleotide is an organic molecule made up of a nucleotide base, a five-carbon sugar (ribose or deoxyribose) and at least one phosphate group. Nucleotides make up the basic units of DNA and RNA molecules.