In humans, cholesterol itself can be synthesized in the body, which is in the liver, cortex, adrenal, skin, intestine, testis, stomach, muscle, adipose tissue, and brain. Approximately 17 percent of the dry weight of the brain composed of cholesterol. Thus, no cholesterol, brain structure might not formed.
Cholesterol is a product of the metabolism of typical animals. Cholesterol is found only in foods of animal origin such as meat, fish, eggs, milk, brain, and innards. Judging from their chemical structure, cholesterol is a steroid group, ie a substance which belongs to the class of lipids.
Although it is considered dangerous, but cholesterol is needed by the body. The average human need 1100 milligrams of cholesterol per day to maintain cell walls and other physiological functions. Of these 25-40 percent (200-300 mg) is normally derived from food and the rest is synthesized by the body.
If the amount of cholesterol in the body is less, the synthesis of cholesterol in the liver and intestine increased to meet the needs of other tissues and organs. Conversely, if the amount of cholesterol in the diet increased, the synthesis of cholesterol in the liver and intestine decreased.
Although the body can synthesize the cholesterol, the cholesterol that comes from food plays an important role because it is the major sterol in the human body. As well as components of cell surface and intracellular membranes.
Research on mice shows, if there is only 0.05 percent of the cholesterol in foods, 70-80 percent of the body's cholesterol is synthesized in the liver, small intestine, and adrenal glands. If the content of cholesterol in the diet up to 2 percent, the biosynthesis of cholesterol in the body decreased to 10-30 per cent.
Cholesterol is needed by the body such as in the synthesis of bile acids needed for digestion of fat or oil, the synthesis of vitamin D, and as a component of the cell membrane. Cholesterol has a very important role in the body because it is not only the membrane-forming cells, but also other common biosynthetic precursor, including sex hormone bile acids.
Cholesterol is a precursor of bile acids expenditures which are synthesized in the liver and serves to absorb triglycerides (triasilogliserol) and fat soluble vitamins from food, as well as precursors of steroid hormones, estrogen and testosterone.
Another role of cholesterol, which helps nerve cells to function. If no cholesterol, coordination of gestures and speech will be disrupted.
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
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.
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