Generally, peptides contain two to nine amino acids. Depending on the number of amino acids in the peptide, there are various names for the peptide, such as dipeptide, tripeptide, tetrapeptide, pentapeptide, etc. Peptides composed of three or more amino acid molecules are called peptides, with a molecular weight below 10000 Da. They can pass through semi permeable membranes and are not precipitated by trichloroacetic acid and ammonium sulfate. Some literature also refers to peptides composed of 2-10 amino acids as oligopeptides (small molecule peptides); Peptides composed of 10 to 50 amino acids are called peptides; A peptide composed of 50 or more amino acids is called a protein, in other words, a protein is sometimes referred to as a polypeptide. Peptides, also known as peptides, were discovered in the 20th century.
