How many standard amino acids are genetically encoded, and what is the significance of their side chains?

• A. 18 standard amino acids; side chains barely affect protein behavior.
• B. 20 standard amino acids; side chains determine properties and protein structure.
• C. 21 standard amino acids; side chains determine only whether proteins fold.
• D. 20 standard amino acids; side chains are identical across all amino acids.

Answer: (B)