Advanced Placement (AP) Biology Practice Exam

What type of bond connects amino acids together in a protein?

1. Ionic bond

2. Peptide bond

3. Hydrogen bond

4. Covalent bond

The correct answer is: Peptide bond

A peptide bond is the specific type of covalent bond that links amino acids together to form proteins. When amino acids react during a dehydration synthesis reaction, the carboxyl group of one amino acid bonds with the amino group of another, resulting in the release of a water molecule. This bond forms a peptide linkage, creating a dipeptide, and as more amino acids are added, a polypeptide and eventually a functional protein are formed. Understanding that peptide bonds are a subtype of covalent bonds clarifies why the designation of peptide bond is critical in the context of proteins. While ionic bonds involve the transfer of electrons and hydrogen bonds involve partial charges between molecules, neither directly connects amino acids in the formation of protein structures. Therefore, recognizing the unique role of peptide bonds in protein synthesis is essential to understanding protein structure and function.