Protein
A large, complex molecule composed of one or more polypeptide chains folded into a specific three-dimensional structure. Proteins perform essential functions in the body including catalysing reactions, transporting molecules, and providing structural support. Some therapeutic compounds, such as growth hormone, are technically proteins rather than peptides.
Technical Context
Proteins are distinguished from peptides by size and structural complexity. While peptides are generally short chains under 50 amino acids, proteins are larger molecules that adopt stable three-dimensional conformations through secondary structure (alpha-helices, beta-sheets), tertiary structure (overall 3D shape), and sometimes quaternary structure (multi-subunit assemblies). Some therapeutic compounds, such as somatropin (22,124 Da), are proteins rather than peptides. This distinction matters for manufacturing — proteins typically require recombinant DNA technology rather than chemical synthesis — and for regulatory classification under the BLA rather than NDA pathway.