Standard Amino Acids Twenty standard a-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 Chapter 24 6 Chapter 24 6 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