USA Biology Olympiad (USABO) Practice Exam

Which two functional groups are consistently found in all amino acids?

1. Ketone and hydroxyl

2. Aldehyde and carboxyl

3. Carboxyl and amine

4. Hydroxyl and phosphate

The correct answer is: Carboxyl and amine

Amino acids are the building blocks of proteins and share a common structure that includes two specific functional groups that are essential for their identity. All amino acids contain a carboxyl group (-COOH), which is known for its acidic properties. This group gives amino acids the ability to donate a proton (H+) and contribute to the overall charge of the molecule. In addition to the carboxyl group, all amino acids also include an amine group (-NH2). The amine group can accept a proton, making the amino acid a basic compound. This dual presence of the carboxyl and amine groups is what defines amino acids and is critical for the formation of peptide bonds during protein synthesis. These features are crucial for the biological functions of amino acids, as they allow them to act both as acids and bases, facilitating their roles in biochemical reactions and structures.