Cholesterol is a macromolecule that is classified as a lipid. Besides steroids, such as cholesterol, lipids include fats, oils, waxes and phospholipids. Lipids are composed of carbon, hydrogen and oxygen.
Lipids have a hydrocarbon side chain. Based on the nature of this chain, the lipid may be further classified as saturated or unsaturated. Saturated lipids have no double bonds in the molecule, while unsaturated lipids have double bonds. The terms "saturated," "mono-unsaturated" and "poly-unsaturated" refer to the number of hydrogens attached to the molecule. Lipids from plant sources are unsaturated. Lipids in biological membranes are found as double layers and are amphipathic in nature.