What best describes the peptide bond?

• A. The covalent linkage between two amino acids in a polypeptide; formed by a dehydration reaction
• B. A noncovalent interaction between amino acid side chains
• C. The ionic bond between amino and carboxyl groups
• D. A hydrogen bond stabilizing alpha helices

Answer: (A)

The major idea here is how amino acids connect to build a protein. A peptide bond is a covalent linkage that joins the carboxyl carbon of one amino acid to the amino nitrogen of the next amino acid in a polypeptide. This connection forms through a dehydration (condensation) reaction, as a water molecule is released. That covalent amide bond is the backbone of proteins, not a noncovalent interaction or an ionic or hydrogen-bond interaction. The bond also has partial double-bond character from resonance, making it planar and restricting rotation, which helps shape the protein’s overall structure.