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 =>