Cholesterol strcture and function
Download as PPTX, PDF4 likes15,712 views
This document discusses cholesterol, including its structure, properties, sources, and importance. Cholesterol has the molecular formula C27H45OH and possesses a cyclopentano perhydro phenanthrene nucleus. It is synthesized endogenously in the body and obtained exogenously through diet. Cholesterol is an important component of cell membranes and is a precursor for bile acids, steroid hormones like estrogen and testosterone, and vitamin D3. It occurs both in free and esterified forms in the body and liver plays a key role in regulating cholesterol levels.
Cholesterol strcture and function
- 2. CHOLESTEROL • Structure: Cholesterol is the most important sterol in human body. Its molecular formula is C27H45OH. • It possesses “cyclopentano per hydro phenanthrene nucleus”. • It has an –OH group at C3. • It has an unsaturated double bond between C5 and C6. • It has two –CH3 groups at C10 and C13. • It has an eight carbon side chain attached to C17.
- 4. CHOLESTEROL • Properties: The name cholesterol is derived from the Greek word meaning solid bile. • It occurs as a white or faintly yellow, almost odourless, pearly leaflets or granules. • It is insoluble in water, sparingly soluble in alcohol and soluble in ether, chloroform, hot alcohol, ethyl acetate and vegetable oils. • It easily crystallises from such solutions in colourless
- 5. CHOLESTEROL • Source • Exogenous: Dietary cholesterol, approximately 0.3 gm/day. Diet rich in cholesterol are butter, cream, milk, egg yolk, meat, etc. A hen’s egg weighing 2 oz gives 250 mg cholesterol • Endogenous: Synthesised in the body from acetyl CoA, approximately 1.0 gm/day. • Occurrence: It is widely present in body tissues. nervous tissue 2 per cent, in the liver about 0.3 per cent, skin 0.3 per cent and intestinal mucosa 0.2 per cent, certain endocrine glands
- 6. CHOLESTEROL • Forms of cholesterol: • Cholesterol occurs both in free form and in ester form, in which it is esterified with fatty acids at –OH group at C3 position. • The ester form of cholesterol is also referred as bound form.
- 7. CHOLESTEROL 1. Cell membranes: Cholesterol is a component of membranes and has a modulating effect on the fluid state of the membrane. 2. Nerve conduction: Cholesterol has an insulating effect on nerve fibers. 3. Bile acids and bile salts are derived from cholesterol. Bile salts are important for fat absorption. 4. Steroid hormones: Glucocorticoids, androgens and estrogens are from cholesterol. 5. Vitamin D3 is from 7-dehydro-cholesterol. 6. Esterification: The OH group of cholesterol is esterified to fatty acids to form cholesterol esters. This esterification occurs in the body by transfer of a PUFA moiety by lecithin cholesterol acyl transferase
- 8. Biomedical Importance of Cholesterol
- 10. CHOLESTEROL Liver and Cholesterol • The liver has a major role in controlling the plasma levels of LDL cholesterol. 1. Liver synthesises cholesterol 2. Liver removes cholesterol from Lp remnants. 3. Liver is the only organ that can excrete cholesterol through bile. 4. Liver converts cholesterol to bile acids. • Esterification of cholesterol: • Some cholesterol esters are formed in tissues by the transfer of acyl groups from acyl-CoA to cholesterol by acyl transferases.
- 11. CHOLESTEROL • Colour Reactions of Sterols • (a) Liebermann-Burchard reaction: A chloroform solution of a sterol, when treated with acetic anhydride and conc. H2SO4 gives a grass-green colour. This reaction forms the basis for a colorimetric estimation of cholesterol by Sackett’s method. • (b) Salkowski test: When a chloroform solution of the sterol is treated with an equal volume of conc. H2SO4 develops a red to purple colour. • (c) Zak’s reaction: When glacial acetic acid, (aldehyde free), solution of cholesterol is treated with ferric chloride and conc. H2SO4, produces a red colour. This reaction forms a basis for the colorimetric estimation of cholesterol (Zak’s method).