COOH Leudne (Leu,1) Proline (Pro,P) There are the one- HN-C-H RN+C-H letter and three-letter Alaine (Al A) Valine (Val,V) codes used to denote (b)Folar,unchargod amino acids.For each amino acid,the D00 ball-and-stick (left) and space-filling e(. (right)models show only the side chain HNT-C-HThere are the one￾letter and three-letter codes used to denote amino acids. For each amino acid, the ball-and-stick (left) and space-filling (right) models show only the side chain