What type of bond links amino acids to form proteins?

• A. Glycosidic bonds
• B. Ionic bonds
• C. Hydrogen bonds
• D. Peptide bonds

Answer: (D)

Amino acids are linked into proteins by peptide bonds, covalent linkages formed through a condensation reaction between the carboxyl group of one amino acid and the amino group of the next. This creates an amide bond that joins the amino acids into a polypeptide chain—the protein’s backbone. The peptide bond is strong and has partial double-bond character due to resonance, making it planar and restricting rotation, which helps define the chain’s orientation and the protein’s primary structure. Other bond types mentioned don’t link amino acids into the protein chain: glycosidic bonds connect sugars, ionic bonds are electrostatic attractions, and hydrogen bonds stabilize folded structures rather than form the main backbone.