What is the concept of peptides? A peptide (peptide) is a compound consisting of two or more amino acids linked by peptide bonds. It represents a novel type of nutrition that lies between large molecular proteins and amino acids, characterized by high activity, easy absorption, and significant physiological efficacy. Peptides are generally composed of L-type α-amino acids, also known as polypeptides, which are an important class of active substances in living organisms. Their chemical structure is shown in the figure below.
R represents the side chains of different amino acids. Due to the varying composition and sequence of amino acids, different peptides are formed. Compounds made up of two amino acids linked by a peptide bond are called "dipeptides," and so on; a compound made up of nine amino acids is called a "nonapeptide." A peptide made up of multiple amino acids (usually around 50, or sometimes up to 100) is called a polypeptide. The individual amino acid units that make up the polypeptide are referred to as "amino acid residues." Peptide bonds link the amino acids head-to-tail.
Only molecules with molecular weights ranging from 5000 to 180 can be called "peptides." Peptides with molecular weights ranging from 5000 to 3000 are called "large peptides"; those with molecular weights ranging from 3000 to 1000 are called "polypeptides," while those with molecular weights ranging from 1000 to 180 are called "small peptides," "oligopeptides," or "low molecular weight peptides." These are also known as small molecule active polypeptides and usually consist of 2 to 6 amino acids.