Cholesterol

Cholesterol is a sterol lipid with the molecular formula C₂₇H₄₆O and molar mass of 386.65 g/mol, appearing as a white, waxy, crystalline powder. It features a tetracyclic steroid nucleus (cyclopentanoperhydrophenanthrene ring system) with a double bond between carbons 5 and 6, a hydroxyl group at the 3β position, and an eight-carbon hydrocarbon side chain at carbon 17. The compound has a melting point of 148-150°C, density of 1.052 g/cm³, and is practically insoluble in water but soluble in organic solvents like chloroform and ethanol.​

Structurally amphipathic, cholesterol's polar hydroxyl group orients toward the aqueous environment while its nonpolar rings and tail embed in lipid bilayers, modulating membrane fluidity, packing, and permeability in animal cells. It serves as a precursor for bile acids, vitamin D, and steroid hormones (e.g., cortisol, estrogen, testosterone) via the mevalonate pathway, starting from acetyl-CoA.​

Endogenously synthesized mainly in the liver, it is also dietary from animal products; excess levels contribute to atherosclerosis, managed by statins targeting HMG-CoA reductase.​