which are the 20 known amino acids?
['alanine - ala - A (gif, interactive)', 'arginine - arg - R (gif, interactive)', 'asparagine - asn - N (gif, interactive)', 'aspartic acid - asp - D (gif, interactive)', 'cysteine - cys - C (gif, interactive)', 'glutamine - gln - Q (gif, interactive)', 'glutamic acid - glu - E (gif, interactive)', 'glycine - gly - G (gif, interactive)']