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Hydrophobicity and Cholesterol

As the major sterol, or steroid alcohol, in the body, cholesterol is essential to human health. It is hydrophobic by nature and raises the risk of heart disease when present in excess in the blood (hypercholesterolemia).

  1. Definition

    • Hydrophobicity means insoluble in water. As a substance that does not readily dissolve in liquids, cholesterol can accumulate and block blood vessels unless it is removed from the bloodstream.

    Sources

    • The body (mainly the liver) typically makes all the cholesterol it needs on a daily basis. Additional sources are foods of animal origin, especially those containing saturated and trans-fats.

    Chemical Structure

    • Cholesterol owes its hydrophobicity to its chemical structure. It consists of four hydrophobic rings, with an eight-carbon hydrocarbon chain, hydroxyl group and double bond between carbon atoms.

    Cholesteryl Ester

    • Blood cholesterol mostly exists as cholesteryl ester, which makes its structure more hydrophobic than free cholesterol. Cholesteryl esters are not normally found in cell membranes and only in small quantities inside cells.

    Transport

    • Because cholesterol and other fats cannot dissolve in the blood, they need to be transformed in the bile, or associated with special carriers called lipoproteins. The major types of lipoproteins are: low-density lipoprotein (LDL, or "bad" cholesterol) and high-density lipoprotein (HDL, or "good" cholesterol).

    Degradation

    • Because the hydrophobic ring structure of cholesterol cannot be broken down to water and carbon dioxide, excess cholesterol must be converted to bile acids and bile salts in order to be eliminated from the body. Bacteria also modify some cholesterol before excretion from the body.

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