What makes each amino acid unique?

• A. The presence of an amino group
• B. The side chain ($R$ group) attached to the alpha carbon
• C. The peptide bond formation
• D. The presence of a carboxyl group

Answer: (B)

Verified step by step guidance

1. Understand that amino acids are the building blocks of proteins, each consisting of a central (alpha) carbon atom bonded to four different groups: an amino group (-NH₂), a carboxyl group (-COOH), a hydrogen atom, and a variable side chain (R group).
2. Recognize that the amino group and the carboxyl group are common to all amino acids, providing the basic structure necessary for peptide bond formation.
3. Identify that the side chain, or R group, is the component that varies among different amino acids, giving each one its unique properties and characteristics.
4. Consider how the side chain affects the amino acid's chemical behavior, such as its polarity, charge, and ability to interact with other molecules, which in turn influences protein structure and function.
5. Conclude that the uniqueness of each amino acid is primarily due to the distinct side chain (R group) attached to the alpha carbon, which differentiates one amino acid from another.