Fats and oils are the major components of cell membranes and are said to be lipids. Lipid is the compound which form the double-layered surface of all cells (lipid bilayer). There are three major classes that membrane lipids are divided into: phospholipids (made of four components: fatty acids, phosphate and alcohol , glycolipids (sugar-containing lipids) and cholesterol (lipid with a structure quite different from that of phospholipids).