What Is Cholesterol?
Cholesterol is an organic compound with a steroidal structure. It is an essential component of cell membranes in animal cells. It is also a raw material for steroid hormones, sex hormones, and bile acids that promote fat absorption.
Since it is insoluble in blood, it must be transported in the form of particles called lipoproteins. Lipoproteins include LDL (low-density lipoprotein) and HDL (high-density lipoprotein), and the corresponding cholesterol is called LDL cholesterol and HDL cholesterol, respectively.
Uses of Cholesterol
The main uses of cholesterol are as a raw material for cosmetics, pharmaceuticals, and industrial products.
In cosmetics, cholesterol is used in creams and emulsions, and in pharmaceuticals, it is used in oral and topical formulations (e.g., anti-inflammatory ointments).
The esters of cholesterol and fatty acids have liquid crystalline properties. This is applied to industrial products in the form of liquid crystal materials called cholesteric liquid crystals. Cholesteric liquid crystals are used in electronic paper display technology and temperature sensors.
Properties of Cholesterol
Cholesterol is a white to pale yellow crystal with chemical formula C27H46O and a molecular weight of 386.65. It is lipophilic, nearly insoluble in water, and has a melting point of 149℃.
The coloring reaction can be seen in the Salkowski reaction and the Liebermann-Burchard reaction. In the Salkowski reaction, cholesterol is dissolved in chloroform and mixed with concentrated sulfuric acid. The chloroform layer turns red and the sulfuric acid layer turns yellow and fluoresces green.
In the Liebermann-Burchard reaction, cholesterol is dissolved in chloroform, a few drops of acetic anhydride are added, and then a few drops of concentrated sulfuric acid are added and mixed. The chloroform layer turns rose-colored and eventually turns green.
Structure of Cholesterol
Cholesterol has a steroidal skeleton consisting of three six-membered rings and one five-membered ring.
Cholesterol is a sterol because it has a hydroxyl group at position 3 of the steroid skeleton.
Other Information on Cholesterol
1. How It Is Synthesized in the Body
Cholesterol is mainly synthesized in the liver from the three major nutrients (carbohydrates, proteins, and fats). Acetyl coenzyme A is the first product of the breakdown of the three macronutrients.
Acetyl CoA is converted to mevalonic acid by the action of several enzymes. Mevalonic acid undergoes several chemical reactions to produce squalene, which has a steroidal skeleton. Squalene undergoes several more chemical reactions and is finally converted to cholesterol.
2. Absorption in the Body
Cholesterol ingested from food is absorbed in the small intestinevia a protein called cholesterol transporter.
3. Action in the Body (LDL Cholesterol)
LDL cholesterol carries cholesterol to the cells and tissues of the body. When the amount of LDL cholesterol in the blood increases due to some abnormality, LDL cholesterol accumulates and oxidizes in the walls of blood vessels. The result is atherosclerosis.
LDL cholesterol is also called bad cholesterol because it promotes atherosclerosis.
4. Action in the Body (HDL Cholesterol)
The function of HDL cholesterol is to collect unwanted cholesterol in cells and cholesterol deposited in blood vessel walls and return it to the liver.
HDL cholesterol is also called good cholesterol because it inhibits atherosclerosis.
5. Criteria for Blood Cholesterol Levels
When the levels of LDL cholesterol and HDL cholesterol meet the following criteria, dyslipidemia is suspected.
- LDL Cholesterol: 140 mg/dl or higher
- HDL Cholesterol: less than 40 mg/dl