Amino acids condense to produce peptides. Generally condensation reaction occurs between a primer amino acid or peptide and another amino acid. Molecule of water is eliminated. The bond thus formed (- NHCO -) is actually an amide bond which is popularly known as peptide bond or peptide linkage. Chain containing two amino acids linked by a peptide bond is called dipeptide. There are three amino acids in a tripeptide, a few in oligopeptide and numerous in a polypeptide.