Peptides vs. Proteins

The line between peptides and proteins is drawn by chain length and structural complexity. By convention, molecules with fewer than 50 amino acids are called peptides. Longer chains that fold into specific three-dimensional shapes are called proteins.

Peptides tend to be more flexible and less structured than proteins. Proteins often adopt specific folded conformations stabilized by hydrogen bonds, disulfide bridges, and hydrophobic interactions.

Despite size differences, peptides and proteins can perform overlapping functions. Insulin (51 amino acids) is sometimes classified as a small protein; many peptide hormones span 10-40 residues.