Cholesterol.pptx

Cholesterol is a waxy substance found in your blood. Your body needs cholesterol to build healthy cells, but high levels of cholesterol can increase your risk of heart disease.

1. Cholesterol

2. Specific Learning objectives At the end of the lecture students will be able to Define cholesterol. Explain the structure of cholesterol. Describe the properties of cholesterol. Explain the functions of cholesterol. Explain the compounds formed from cholesterol

3. Introduction The word cholesterol is derived from Greek words, chole = bile; steros = solid; ol = alcohol. Exclusively found in animal & most abundant animal sterol. Widely distributed in all cells & major component of membranes and Lipoproteins.

4. Cont…. Cholesterol comes from two sources

5. Definition Cholesterol is  a structural component of cell membranes and serves as a building block for synthesizing various steroid hormones, vitamin D, and bile acids .

6. Structure 27 carbon compound Double bond at C5-C6 Hydroxyl g roup (OH group) at C3 8 carbon side chain at C17 Total 5 methyl group molecular formula of C27H45OH.

7. Properties Yellowish crystalline solid Isolated cholesterol is a white , flaky solid that is insoluble in aqueous environments [Strongly hydrophobic ] Soluble in organic solvent like chloroform, benzene, ether etc.

8. Functions Cholesterol is essential to life. It is a structural component of cell membrane . Cholesterol is the precursor for the synthesis of all other steroids in the body . These include steroid hormones, vitamin D and bile acids.

9. Cont… Essential ingredient in structure of Lipoprotein. Transportation of fatty acid- . Fatty acids are transported to liver as cholesteryl esters for oxidation . Insulating cover for transmission of electric impulse in nervous tissue.

10. I . Synthesis of bile acids The bile acids possess 24 carbon atoms , 2 or 3 hydroxyl groups in the steroid nucleus and a side chain ending in carboxyl group . The bile acids are amphipathic in nature since they possess both polar and non-polar groups . They serve as emulsifying agents in the intestine and actively participate in the digestion and absorption of lipids. COMPUNDS FORMED FROM CHOLESTEROL

11. Cont…. The synthesis of primary bile acids takes place in the liver and involves a series of reactions. The step catalysed by 7 D-hydroxylase is inhibited by bile acids and this is the rate limiting reaction. Cholic acid and chenodeoxycholic acid are the primary bile acids and the former is found in the largest amount in bile.

12. Cont…. On conjugation with glycine or taurine , conjugated bile acids (glycocholic acid, taurocholic acid etc.) are formed which are more efficient in their function as surfactants . In the bile, the conjugated bile acids exist as sodium and potassium salts which are known as bile salts.

13. Cont…. In the intestine , a portion of primary bile acids undergoes deconjugation and dehydroxylation to form secondary bile acids ( deoxycholic acid and lithocholic acid). These reactions are catalysed by bacterial enzymes in the intestine.

14. Cholelithiasis Bile salts and phospholipids are responsible for keeping the cholesterol in bile in a soluble state . Due to their deficiency (particularly bile salts), cholesterol crystals precipitate in the gall bladder often resulting in cholelithiasis—cholesterol gall stone disease . Cholelithiasis may be due to defective absorption of bile salts from the intestine, impairment in liver function, obstruction of biliary tract etc.

15. II. Synthesis of steroid hormones from cholesterol Cholesterol is the precursor for the synthesis of all the five classes of steroid hormones ( a) Glucocorticoids (e.g. cortisol) ( b) Mineralocorticoids (e.g. aldosterone) ( c) Progestins (e.g. progesterone ) (d) Androgens (e.g. testosterone) (e) Estrogens (e.g. estradiol).

16. III. Synthesis of vitamin D 7-Dehydrocholesterol , an intermediate in the synthesis of cholesterol, is converted to cholecalciferol ( vitamin D3) by ultraviolet rays in the skin .

17. Expected Questions Short Explain the compounds formed from cholesterol.

18. THANK YOU Eat good diet to keep heart Healthy