Cholesterol biosynthesis

Cholesterol is synthesized in the liver, adrenal cortex, intestine, skin, and aorta. The synthesis takes place in the cytosol and microsomes cell network.



Stages as follows:

1. The formation of acetyl CoA mevalonic

2. Formation of squalene from mevalonic

3. Change of squalene to lanosterol which then turned into cholesterol



Sequence of reactions:

1. Formation of acetyl CoA. Acetic acid molecule is activated to acetyl CoA by using energy derived from ATP and is catalyzed by the enzyme acetyl-CoA synthetase. Mg as a cofactor.

2. Two acetyl-CoA molecules condense to form asetoasetil CoA. Enzymes that work here are tiolase.

3. Asetoasetil CoA condenses with acetyl CoA molecules to form HMG CoA. The enzyme is HMG CoA synthetase catalyses. This process requires water and produce byproducts such as CoA-SH.

4. HMG CoA reductase is reduced by NADPH and with the assistance of H. The results will form mevalonic.

5. Mevalonic have 3 rows of reactions involving phosphorylation by 3 ATP and removes one carbon atom mevalonat. Isoprenoid units formed. Byproducts such as carbon dioxide and water.

6. Two units of isoprenoid pyrophosphate condense to form a 10-atom geranil C.

7. The isoprenoid molecules condense further to form farnesil geranil pyrophosphate pyrophosphate.

8. Two molecules combine to form squalene pyrophosphate farnesil with 30 atom C.

9. Ring closure to form lanosterol.

10. Lanosterol converted into a 14-desmetil lanosterol (loss of a methyl group) zimosterol → → → desmosterol cholesterol.



Enzymes are important in the synthesis of cholesterol is HMG CoA reductase. This enzyme is inhibited by high-cholesterol foods and feedback inhibition. In extrahepatic tissues, HMG CoA reductase is inhibited by cholesterol in LDL. In the intestinal tissue, this enzyme is inhibited by bile acids. Thyroid hormone and insulin also played a role in the inhibition of these enzymes work.

Cholesterol synthesis

Cholesterol is synthesized is part of the cholesterol in the body. Only a small fraction of cholesterol that comes from food.

From food: 300-750 mg

Synthesis of body / endogenous: 650-1000 mg