The molecular formula of cholesterol is C27 H46 O with a molecular weight of 386.65 grams per mole. The International Union of Pure and Applied Chemistry (IUPAC) name is: (3β)-cholest-5-en-3-ol. Being a member of the sterol class, the primary structure of cholesterol is a cyclopentanoperhydrophenanthrene or “sterane” composition that includes three 6-carbon rings and one of 5. Initially called “cholesterine”, the common name is now cholesterol with khole: bile, stereos: solid (both Greek origin) and -ol to denote the attached hydroxyl alcohol.
Properties of Cholesterol
While classified as a lipid, cholesterol has weak amphipathic properties. This is due to the polar nature of the hydroxyl group on the A ring and the hydrophobic characteristics of the ring structure with accompanying hydrocarbon tail. Having a flat profile, cholesterol inserts well into the lipid bilayers of a cell membrane, with the polar region sticking out to interact with the phospholipid portion of the bilayer and the hydrophobic portions oriented inward. Cholesterol in cell membranes has a stabilizing effect, reducing permeability while making them more resistant to physical damage and temperature change.
Cholesterol in Human Physiology
In the human body, more cholesterol is synthesized by cells than acquired through dietary sources. Only about half of ingested cholesterol is actually absorbed and incorporated by the body. Absorbed cholesterol is combined with fats in the form of triglycerides and a special carrier protein in cells of the small intestine. This lipid package then transits the lymphatic and circulatory systems before being further processed by the liver. Regardless of origin, cholesterol is then used as a substrate for steroidal hormones and a component of cell structure. Several types of protein are involved in the transport of cholesterol to and from the liver. Serum cholesterol levels are evaluated by the fractions of it bound to these carrier proteins and designated as high density lipoproteins (HDL), low density (LDL) and very low density (VLDL).
Regulation and Elimination of Cholesterol
While many cells may create cholesterol, the liver synthesizes about 25% and is one of the few organs capable of eliminating it. The liver rids the body of excess cholesterol by conjugating it with amino acids to create bile salts. Bile is collected and stored in the gallbladder until released into the digestive tract. The gallbladder secretes bile into the small intestine in response to hormonal signaling associated with dietary fat intake and is instrumental in the absorption of lipids. After fulfilling this responsibility some of the bile is reabsorbed and some remains attached to dietary fiber.
Plants and Cholesterol
Contrary to popular thought, researchers have confirmed that plants and algae also synthesize cholesterol, sometimes in quite substantial amounts. Many higher plants maintain up to 5% of their sterols in cholesterol-form with higher concentrations in chloropasts, shoots, and pollen. Some, like European false flax (Camelina sativa), contain unusually large amounts of cholesterol ranging upwards of 200 mg cholesterol per kg of plant oil.
Resources
V. Shukla, P. Dutta, and W. Artz, “Camelina oil and its unusual cholesterol content,” Journal of the American Oil Chemists' Society 79, no. 10 (October 1, 2002): 965-969, doi:10.1007/s11746-002-0588-1.
Linda T. Welson, Triglycerides And Cholesterol Research, 1st ed. (Nova Biomedical Books, 2006).
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