Which functional groups are characteristic of amino acids?

Which functional groups are characteristic of amino acids?

• A. Carboxyl and amino groups
• B. Hydroxyl and phosphate groups
• C. Methyl and amino groups
• D. Aldehyde and carboxyl groups

Answer: (A)

The defining feature of amino acids is the presence of both an amino group and a carboxyl group attached to the same central carbon. The amino group can accept a proton, giving it a positive charge, while the carboxyl group can donate a proton, giving it a negative charge. At physiological pH, these groups typically exist as a zwitterion with both charges, which is a hallmark of amino acids and drives their ability to form peptide bonds and participate in protein structure. Other functional groups like hydroxyl or phosphate, or methyl and aldehyde, are not universal features of amino acids, so they don’t define what amino acids are.

The defining feature of amino acids is the presence of both an amino group and a carboxyl group attached to the same central carbon. The amino group can accept a proton, giving it a positive charge, while the carboxyl group can donate a proton, giving it a negative charge. At physiological pH, these groups typically exist as a zwitterion with both charges, which is a hallmark of amino acids and drives their ability to form peptide bonds and participate in protein structure. Other functional groups like hydroxyl or phosphate, or methyl and aldehyde, are not universal features of amino acids, so they don’t define what amino acids are.