What structural feature do all amino acids have in common?

• A. A $\mathrm{phosphate} \mathrm{group}$ and a $\mathrm{hydroxyl} \mathrm{group}$
• B. A $\mathrm{carboxyl} \mathrm{group}$ and an $\mathrm{amino} \mathrm{group}$
• C. A $\mathrm{sulfhydryl} \mathrm{group}$ and a $\mathrm{methyl} \mathrm{group}$
• D. A $\mathrm{benzene} \mathrm{ring}$ and a $\mathrm{carbonyl} \mathrm{group}$

Answer: (B)

Verified step by step guidance

1. Identify the common structural features of amino acids. Amino acids are organic compounds that serve as the building blocks of proteins.
2. Recognize that all amino acids have two key functional groups: an amino group (-NH₂) and a carboxyl group (-COOH).
3. Understand that the amino group is a basic functional group, while the carboxyl group is acidic, allowing amino acids to act as both acids and bases.
4. Note that the presence of both an amino group and a carboxyl group is what distinguishes amino acids from other organic molecules.
5. Conclude that the correct structural feature common to all amino acids is the presence of both a carboxyl group and an amino group.