An amino acid is an organic compound made up of a basic amino group, an acidic carboxyl group, and a side chain that varies between different amino acids. Lysine (6 letters) is an essential amino acid that helps the body absorb calcium and build muscle. DOPA (4 letters) is an amino acid precursor to dopamine, a neurotransmitter involved in reward and pleasure. Leucine (7 letters) is an essential branched-chain amino acid that helps regulate blood sugar levels and promote muscle growth. PROTEIN (7 letters) is a macronutrient composed of amino acids that are essential for growth and repair of tissues. Proline (7 letters) is an amino acid that helps form collagen, which is important for skin elasticity and joint health. Serine (6 letters) is an amino acid that helps regulate metabolism and is important for proper brain function. Glycine (7 letters) is an amino acid that helps form proteins and is important for healthy skin and connective tissue. Arginine (8 letters) is an amino acid that helps the body remove waste products and is important for immune system function.