Cholesterol. Surface maps (wire-frame and colour- coded) of the electrostatic potential around a cholesterol molecule (C27.H46.O). The green area consists of hydrocarbon rings. A hydrocarbon chain leads off to right. The oxygen atom (not colour- coded) is at the bottom left end of the molecule. Cholesterol is a lipid, a fat-like substance, and is a sterol, a type of alcohol. It is an important cell chemical, and plays a crucial role in synthesising bile salts and hormones, and also in transporting fats in the blood. High blood levels of cholesterol are thought to raise the risk of atherosclerosis, the build-up of fatty deposits on artery walls, a major cause of heart attacks.