Amino acids are the building blocks of proteins, which are essential for life. DOPA (4 letters) is an amino acid that is a precursor to dopamine, a neurotransmitter. Proline (7 letters) is an amino acid that helps form the secondary structure of proteins. Tyrosine (8 letters) is an amino acid that is a precursor to hormones and neurotransmitters. Serine (6 letters) is an amino acid that is involved in many metabolic pathways. Glycine (7 letters) is an amino acid that is the simplest of all the amino acids. Arginine (8 letters) is an amino acid that is involved in many metabolic pathways. PROTEIN (7 letters) is a macromolecule made up of amino acids. Threonine (9 letters) is an amino acid that is involved in PROTEIN synthesis. Valine (6 letters) is an amino acid that is essential for growth and development. Leu (3 letters) is an abbreviation for leucine, an essential amino acid. Lysine (6 letters) is an amino acid that is essential for growth and development. Leucine (7 letters) is an essential amino acid that is involved in PROTEIN synthesis. Creatine (8 letters) is an amino acid that is involved in energy production.