How is a peptide different from a protein?

Proteins and peptides are both composed of chains of amino acids linked by peptide bonds, but they differ primarily in size, structure, and complexity.123

Key Distinctions

• Size: Peptides are generally smaller, typically consisting of 2 to 50 amino acids. Proteins are larger macromolecules, usually containing 50 or more amino acids, with many ranging into the thousands.123
• Structure: While peptides often have less defined structures, proteins frequently adopt complex, specific conformations known as secondary, tertiary, and quaternary structures.1
• Terminology: Peptides with few amino acids are often called oligopeptides, while longer chains are termed polypeptides. Because proteins are formed from one or more polypeptide chains, they are essentially very large, complex polypeptides.1243

The distinction between a large polypeptide and a protein can be imprecise and is sometimes considered academic, though some authorities define proteins as having a molecular weight greater than 10,000 daltons.43