Computer artwork of the molecule of Proline, technically an amino acid, but regarded as an amino acid due to its important role in protein synthesis. It is considered a non-essential amino acid, which is manufactured mainly from ornithine, glutamine, and glutamate in the liver. Proline is one of the principal amino acids that are needed by the body to build collagen. Atoms are represented as colour-coded spheres: carbon (black), hydrogen (white), nitrogen (blue) and oxygen. Illustration.