- Chemistry of Cholesterol
C27H45OH is the molecular formula of cholesterol. The molecules consist of three regions: a hydrocarbon tail, a hydroxyl group, and a a ring structure region with 4 hydrocarbon rings.
The solubility of the hydroxyl group in water can be attributed to its polar nature. The 4-ring region that also comprises cholesterol is a common ring in all steroids. The rings have a carbon atom at each corner with two hydrogen atoms that extend off the ring. That is why it is called a hydrocarbon ring. The ring region and the tail region cannot dissolve in water, as they are both non-polar (Masterjohn).
- Biosynthesis of Cholesterol
2.1 First step: Synthesis of Mevlonate
Cholesterol synthesis begins with the formation of isopentenyl pyrophosphate from acetyl CoA (Berg et al.). The reaction starts with hydroxy-3-methylglutaryl CoA (HMG CoA) being formed from acetyl CoA and acetoacetyl CoA. This HMG CoA is transformed into mevalonate in the cytosol. This conversion is the committed step in cholesterol synthesis and is catalyzed by the enzyme 3-hydroxy-3-methylglutaryl CoA reductase (HMG-CoA reductase).
2.2 Second Step: Synthesis of Squalene from Six Molecules of Isopentenyl Pyrophosphate (C5)
Isopentenyl pyrophosphate gets converted to squalene by the reaction sequence:
First, geranyl pyrophosphate and farnesyl pyrophosphate are formed from isopentenyl pyrophosphate through a condensation mechanism. Two molecules of farnesyl pyrophosphate in the presence of squalene synthese together form squalene.
2.3 Third Step: Cyclization of Squalene
Finally, cyclization of squalene takes place, resulting in the formation of cholesterol.
- HDl and LDL Cholesterol
Cholesterol is produced by the liver and is a waxy substance. It is required in the body to form vitamin D and some hormones, construct cell walls, and form bile salts that help in the digestion of fat. The liver produces around 1,000 mg of cholesterol per day. Many of the goods we consume also contain cholesterol.
Cholesterol needs to combine with proteins to form lipoproteins to be transported in the body. There are two types of lipoproteins. They are:
- high-density lipoproteins (or HDL) and
- low-density lipoproteins (or LDL).
While HDL is “good cholesterol,” LDL cholesterol is “bad cholesterol.” LDL cholesterol clogs the arteries and causes heart attacks. HDL cholesterol functions by removing cholesterol from the arteries and transporting it back to the liver.
- Dangers of High Cholesterol
Consuming too much cholesterol could be harmful to the body. LDL cholesterol when it gets deposited on the walls of the arteries forms plaque, a hard substance, as time progresses. Plaque leads to a condition called atherosclerosis as it results in narrowing of the arteries and decrease in the blood flow. When atherosclerosis affects the coronary arteries, coronary artery disease results, subjecting a person to high risk of heart attack. When cerebral vascular disease results due to atherosclerosis affecting the blood vessels supplying the brain, stroke is a common risk to the person.
- What Causes High LDL Cholesterol Levels?
- Overweight: High cholesterol levels have been linked to excess weight.
- Heredity: This is a major risk to heart attacks if someone in your family has cholesterol problems.
- Diet: Cholesterol-rich foods pose a high risk to heart disease. After all, you are what you eat, so practice restraint while consuming high-fat foods.
- Age: Cholesterol levels increase as age increases.
Works Cited
- Berg J. M, Tymoczko J. L, and Stryer L. Biochemistry, New York: W H Freeman, 2002, Web. 1 Aug. 2013 <http://www.ncbi.nlm.nih.gov/books/NBK22350/>
