L12 Lipids-III - Chemistry of Steroids and Lipoproteins PDF

L12 Lipids-III CHEMISTRY OF STEROIDS AND LIPOPROTEINS Dr. Salah Omar December 10, 2024 www.gmu.ac.ae College of Health Learning objectives 1. Identify the basic structure of steroids. 2. List the im...

L12 Lipids-III CHEMISTRY OF STEROIDS AND LIPOPROTEINS Dr. Salah Omar December 10, 2024 www.gmu.ac.ae College of Health Learning objectives 1. Identify the basic structure of steroids. 2. List the important compounds derived from cholesterol in the body and give their biological functions. 3. Classify lipoproteins according to their physical and chemical properties. 4. Describe the role of lipoproteins in the transport of lipids.  CHOLESTEROL Component of biomembranes & plasma lipoproteins. Precursor of other steroids. Present in foods of animal origin such as egg, yolk, meat, liver and brain. Cholesterol-ester is the storage form. ( Completely hydrophobic)  FUNCTIONS OF CHOLESTEROL Structural component of cell membranes & lipoproteins. Precursor for other steroids such as steroid hormones, Vitamin D and bile salts.  Bile Acids  End product of cholesterol metabolism in liver. They are polar (water-soluble) derivatives of cholesterol. Contain 2 compound: Cholic acid & Chenodeoxycholic acid. Amphipathic nature (hydrophilic and hydrophobic). Act as efficient detergents and facilitate the digestion.  STEROID HORMONE Production occurs primarily in adrenal glands and gonads. Cholesterol converted to pregnenolone (21 – carbon steroid) Pregnenolone is described as the mother (precursor) of all steroid hormones.  LIPOPROTEINS Complexes which consist of lipids and proteins Lipids are insoluble in aqueous medium. They are transported in blood by the proteins called APOPROTEINS. Apoprotein + Lipid = Lipoprotein  Depending on the density (by ultra centrifuge) lipoproteins are classified into 5 major types. (i) Chycomicrons (ii) Very low density lipoproteins (VLDL) (iii) Intermediate density lipoprotein (IDL) (iv) Low density lipoprotein (LDL) (v) High density lipoprotein (HDL) Lipoproteins with high lipid and low protein content will float on ultra centrifugation; they have low density. Those with high protein and low lipid content will sediment easily and have a high density. (i) CHYLOMICRONS Synthesized in the intestine. Transport dietary TAG to various tissues (adipose tissue and skeletal muscle). They have low density and largest size among the lipoproteins. Composition : Proteins - 2% TAG – 83% PL’s - 7% Cholesterol - 8% (ii) Very Low Density Lipoproteins (VLDL) They are synthesized in the liver They are responsible for the transport of endogenously synthesized TAG’s from liver to various tissues. Composition : Proteins - 10% TAG – 50% PL’s - 18% Cholesterol - 22% (iv) Low Density Lipoproteins (LDL) Most of the LDL particles are derived from VLDL  LDL transports cholesterol from liver to peripheral tissues. They contain maximum amount of cholesterol. LDL concentration in blood has positive correlation with the incidence of atherosclerosis and cardiovascular diseases. LDL is known as ‘BAD CHOLESTEROL’ as it get deposited in tissues and arterial walls. Composition LDL: Proteins - 22% TAG – 10% PL’s (Phospholipids) - 22% Cholesterol - 46% (v) High Density Lipoprotein (HDL) HDL particles takes the cholesterol from peripheral tissues and transport it to the liver for excretion in bile. It removes the cholesterol from the peripheral tissues, it is called as “Good Cholesterol” Composition : Proteins - 33% TAG – 8% PL’s - 29% Cholesterol - 30%