Lipids are hydrophobic or amphipathic small molecules which include fats, waxes, sterols, fat-soluble vitamins (such as vitamins A, D, E and K), monoglycerides, diglycerides and phospholipids. The crucial role of lipids in biological physiology is evident not only in energy storage and structural components of cellular membranes, but also in signal transduction, membrane trafficking and morphogenesis.