Fundamentals · 6 min read

Amino Acids, Peptides, and Proteins: Distinguishing the Three

Amino acids are organic molecules characterized by the presence of both an amino group (-NH2) and a carboxyl group (-COOH), along with a side chain (R group) that confers each amino acid its distinctive chemical behaviour. The 20 standard amino acids encoded by the genetic code serve as the fundamental monomers from which all peptides and proteins are assembled.

With the sole exception of glycine, every amino acid possesses a chiral centre, giving rise to L- and D-stereoisomers. Living systems almost exclusively incorporate L-amino acids, although D-amino acids occur naturally in select organisms and are deliberately introduced in synthetic peptide research to enhance resistance to proteolytic degradation.

A peptide is a short polymer of amino acids joined by peptide bonds -- amide linkages formed through condensation of one residue's carboxyl group with the next residue's amino group. Although there is no rigid cutoff, molecules comprising roughly 50 or fewer amino acid residues are conventionally classified as peptides rather than proteins.

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