Aliphatic Amino Acid Definition

Alanine is an example of an aliphatic amino acid.
Alanine is an example of an aliphatic amino acid. PASIEKA / Getty Images

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.