Memotiva AP Biology Unit 1 Topic 1.4 and 1.5: Proteins, Amino Acids, Peptide Bonds, and Four Levels of Protein Structure

What is the quaternary structure of a protein?

AP Biology Unit 1 Topic 1.4 and 1.5: Proteins, Amino Acids, Peptide Bonds, and Four Levels of Protein Structure

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Nortren·April 11, 2026

What is the quaternary structure of a protein?

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The quaternary structure exists only in proteins made of two or more polypeptide chains, called subunits. It refers to how these subunits assemble into a larger functional unit. Hemoglobin is a classic example, with four subunits that work together to carry oxygen in red blood cells.