Which type of chemical bond links amino acids to form proteins?

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

Answer: (A)

Amino acids are joined into proteins by peptide bonds. This covalent linkage forms when the carboxyl group of one amino acid reacts with the amino group of the next amino acid, releasing a water molecule in a dehydration synthesis step. The result is an amide bond that creates the polypeptide backbone with a directional N-terminus to C-terminus. While the overall protein structure is stabilized by hydrogen bonds and, in some cases, disulfide bridges or ionic interactions between side chains, the bond that directly links amino acids to form the chain is the peptide bond.