Amino acids are organic molecules that combine to form peptides and proteins. There are 20 standard amino acids your body uses to build everything from skin to enzymes to hormones. Peptide names often hint at their amino-acid count: BPC-157 is 15 amino acids, KPV is 3 (lysine-proline-valine), thymosin-α1 is 28. The sequence determines what receptor it binds to and what it does in the body.