text: A protein is any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of long strings of amino acids.\n\nThey are the polymers, with the condensation polymerisation of their subunits(amino acids), joined together by the amide linkage, and the bond is called a peptide bond.\n\nProteins have four types of structures:\nPrimary structure\nSecondary structure\nTertiary structure\nquartenary structure\n\nDue to the peptide bonding, proteins are also referred as polypeptides and are synthesised from the DNA.