Proteins are made up of polypeptides and the polypeptides are made up of amino acids linked by the peptide bonds. The glycosidic linkages are seen in the carbohydrates, the glucose units are linked by these linkages to form disaccharides and polysaccharides. The nucleotides are linked by the phosphodiester linkages and the unsaturated fatty acids are characterised by the C=C double bonds.