Learning Objectives • • • • WHAT IS BIOLOGICAL MOLECULES? • • • • • • • • • • • • • Carbohydrate Carbohydrate Simple Carbohydrate Complex Carbohydrate Protein Lipids Summary DNA Vitamin Molecule Testing FAT • Shake two drops of cooking oil with about 5 cm3 ethanol in a dry test-tube until the fat dissolves. • Pour this solution into a test-tube containing a few cm3 water. A milky white emulsion will form. This shows that the solution contained some fat or oil. SUGAR Heat a little glucose solution with an equal volume of Benedict’s solution in a test-tube. The heating is done by placing the test-tube in a beaker of boiling water or warming it gently over a blue Bunsen flame. However, if this second technique is used, the test-tube should be moved constantly in and out of the Bunsen flame to prevent the liquid boiling and shooting out of the tube. The solution will change from clear blue to cloudy green, then yellow and finally to a red precipitate (deposit) of copper(I) oxide. PROTEIN To a 1% solution of albumen (the protein of egg-white) add 5 cm3 dilute sodium hydroxide (CARE: this solution is caustic), followed by 5 cm3 1% copper sulfate solution. A purple colour indicates protein. If the copper sulfate is run into the food solution without mixing, a violet halo appears where the two liquids come into contact. STARCH • Shake a little starch powder in a test-tube with some warm water to make a suspension. • Add 3 or 4 drops of iodine solution. A dark blue colour should be produced. Molecule Testing FAT REDUCING SUGAR STARCH PROTEIN Molecule Testing VITAMIN C • Draw up 2 cm3 fresh lemon juice into a plastic syringe. • Add this juice drop by drop to 2 cm3 of a 0.1% solution of DCPIP (a blue dye) in a test-tube. The DCPIP will become colourless quite suddenly as the juice is added. The amount of juice added from the syringe should be noted down. • Repeat the experiment but with orange juice in the syringe. If it takes more orange juice than lemon juice to decolourise the DCPIP, the orange juice must contain less vitamin C. Question