Science, Tech, Math › Science Aliphatic Amino Acid Definition Share Flipboard Email Print PASIEKA / Getty Images 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 08, 2019 An amino acid is an organic molecule characterized by having a carboxyl group (-COOH), amino group (-NH2), and side chain. One type of side chain is aliphatic: Aliphatic Amino Acid Definition An aliphatic amino acid is an amino acid containing an aliphatic side chain functional group.Aliphatic amino acids are non-polar and hydrophobic. Hydrophobicity increases as the number of carbon atoms on the hydrocarbon chain increases. Most aliphatic amino acids are found within protein molecules. However, alanine and glycine may be found either inside or outside a protein molecule. Aliphatic Amino Acid Examples Alanine, isoleucine, leucine, proline, and valine, are all aliphatic amino acids. Methionine is sometimes considered an aliphatic amino acid even though the side chain contains a sulfur atom because it is fairly non-reactive like the true aliphatic amino acids.