Cholesterol (C₂₇H₄₆O) — Properties, Uses & Safety

Overview

Cholesterol (C27H46O) is an essential lipid molecule found in every animal cell membrane, where it plays a critical role in maintaining membrane fluidity and structural integrity. With a molar mass of 386.65 g/mol, cholesterol is a waxy, white crystalline solid that is insoluble in water but soluble in organic solvents. Its molecular structure is characteristic of steroids: four fused carbon rings (three six-membered cyclohexane rings and one five-membered cyclopentane ring) forming the steroid nucleus, with a hydroxyl group at one end, a short hydrocarbon tail at the other, and a double bond in one of the rings. This structure makes cholesterol amphipathic — the hydroxyl group interacts with the polar head groups of membrane phospholipids while the rigid ring system and hydrocarbon tail embed in the hydrophobic interior. Cholesterol is synthesized primarily in the liver through a complex biosynthetic pathway starting from acetyl-CoA, with the enzyme HMG-CoA reductase as the rate-limiting step. Statin drugs (like atorvastatin/Lipitor) lower cholesterol by inhibiting this enzyme — one of the most commercially successful drug classes in pharmaceutical history. Cholesterol is also obtained from dietary sources such as eggs, meat, and dairy products. Beyond its structural role in membranes, cholesterol is the precursor to many vital biomolecules: steroid hormones (testosterone, estrogen, cortisol, aldosterone), vitamin D (synthesized when UV light hits cholesterol in the skin), and bile acids (which emulsify dietary fats for digestion). Cholesterol is transported in the blood by lipoproteins — LDL (low-density lipoprotein, often called bad cholesterol) carries cholesterol to tissues, while HDL (high-density lipoprotein, good cholesterol) transports it back to the liver for excretion. Elevated LDL cholesterol is a major risk factor for atherosclerosis and cardiovascular disease, the leading cause of death worldwide. Cholesterol has no GHS hazard classifications. For chemistry students, cholesterol is an excellent compound for studying steroid chemistry and fused ring systems, lipid biochemistry and membrane structure, stereochemistry (cholesterol has eight stereocenters), biosynthetic pathways, and the relationship between molecular structure and biological function. It demonstrates how a single molecule can serve multiple essential roles in the body and how its chemistry connects to major public health concerns.

IUPAC Name

(3beta)-cholest-5-en-3-ol

CAS Number

57-88-5

PubChem CID

5997

Molecular Formula

C₂₇H₄₆O

Molar Mass

386.654 g/mol

State at STP

solid

Appearance

White waxy solid