R1:Classification and tereochemistry of amino acids Standard Amino Acids EST ABF Twenty standard a-amino acids. Differ in side-chain characteristics: ☐-H or alkyl 氨基酸 ☐contains an-OH ☐contains sulfur contains a nonbasic nitrogen ▣has-co0H ☐has a basic nitrogenR1: Classification and stereochemistry of amino acids Standard Amino Acids ❖Twenty standard -amino acids. ❖Differ in side-chain characteristics: ❑-H or alkyl ❑contains an -OH ❑contains sulfur ❑contains a nonbasic nitrogen ❑has -COOH ❑has a basic nitrogen 氨基酸