Amino acids are characterized by their central carbon atom, known as the α-carbon, which is bonded to an amino group (-NH 2), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain ...

The largest group of amino acids have nonpolar side chains. Several other amino acids have side chains with positive or negative charges, while others have polar but uncharged side chains.

Proteins are made of amino acid chains, or polypeptides. Amino acids have a basic backbone made of an amino group and a carboxyl group, and differ in their side-chains.