Lipids Metabolism PDF

LIPIDS METABOLISM Lipids Metabolism Lipids Metabolism: 1-Digestion 2-Absorption 1-Digestion:  Sites: 1-The mouth 2- The stomach 3- The small intestine  Enzymes: 1. the mouth: Saliva contains lingual lipase. It removes short and medium...

LIPIDS METABOLISM Lipids Metabolism Lipids Metabolism: 1-Digestion 2-Absorption 1-Digestion:  Sites: 1-The mouth 2- The stomach 3- The small intestine  Enzymes: 1. the mouth: Saliva contains lingual lipase. It removes short and medium chain F.A from TAG from milk fats. Enzymatic activity of lingual lipase continues in the stomach (stable in an acid PH). 2. the stomach: lingual lipase & gastric lipase act on TAG of milk fats in neonates. Little significance in adults. 2. the small intestine: (bile salts & pancreatic lipase) Bile Salts: they are not enzymes. They act by lowering the surface tension & emulsification of fats. Emulsification: increases the surface area of lipid droplets exposed to digestive enzymes. Bile salts facilitate the action of enzymes (Detergent effect) Pancreatic enzymes (Lipase and co-lipase, Cholesterol esterase & Phospholipase A2): Triacylglycerol digestion: Pancreas secrets lipase & colipase. The pancreatic lipase degrades triacylglycerol at α- position (carbon 1 & 3) removing F.A attached to glycerol by ester bonds at C1 & C3. The products of hydrolysis are 2-monoacylglycerol and free fatty acids FFA  LIPIDS METABOLISM Cholesterol ester digestion: Cholesterol esters are degraded by cholesterol esterase enzyme which needs bile salts for it activation. The products of hydrolysis are cholesterol & FFA. Phospholipid digestion: There are different types of Phospholipase namely A1, A2, C & D. PLA2 removes FA from C2 of phospholipids to yield lysophospholipids. PLA1 removes FA from C1 of lysophospholipid to give glycerophosphoryl base.  LIPIDS METABOLISM 2-Absorption: Micelles Chylomicrons Definition Aggregates of lipid TAGs rich lipoproteins that molecule transport dietary lipids from intestine Size Less than 1.0 µm 1.0 µm in diameter Site Formed in the lumen of Formed in the enterocytes small intestine Composition  Glycerol + cholesterol +  Hydrophobic core: formed long chain FA +bile salts of TAG + cholesterol ester + fat soluble vitamins  Outer layer: formed of  hydrophilic parts to the cholesterol + phospholipids outside & the hydrophobic + apo B-48 parts to the inside. Major Help in absorption of fat Transport the hydrophobic function & fat-soluble vitamins lipids from intestine  LIPIDS METABOLISM I- Metabolism of simple lipid A.Lipogenesis Lipogenesis includes 3 processes: 1. Glycerol synthesis 2. F.A synthesis. 3. Triacylglycerols synthesis 1. Glycerol synthesis: Glycerol is an alcohol containing three hydroxyl groups. It can be synthesized from glyceraldhyde-3- phosphate & dihydroxy acetone phosphate which are intermediate products of glycolysis. 2. F.A synthesis: Definition: formation of fatty acids from acetyl-CoA through the action of enzymes called fatty acid synthases using ATP & NADPH.  De novo synthesis of fatty occurs in cytosol & is called cytosolic.  Fatty acid synthase a multi enzyme complex.  Acetyl-CoA is the substrate  Malonyl CoA is the two-carbon donor for F.A synthesis  Palmitate (16-carbon) is the product. Site: In cytosol in the liver, lactating mammary glands & adipose tissue. Steps: 1- Carboxylation of acetyl- CoA to malonyl- CoA catalyzed by acetyl CoA carboxylase (requires ATP).  LIPIDS METABOLISM 2- Fatty acid synthase: One malonyl-CoA and 2 NADPH are utilized in each reaction sequence by the enzyme complex to add 2 carbons to the chain 3- For the synthesis of 16-carbon palmitic acid reaction sequence is repeated six times. Regulation: Insulin stimulates fatty acid synthesis  Microsomal F.A synthesis (elongation):  palmitate can be elongated (to C22, C24) by the addition of two-carbon units in the smooth endoplasmic reticulum (SER).  Elongation requires a system of separate enzymes.  Malonyl CoA is the two-carbon donor  Needs NADPH. 1. TAGs synthesis: Consist of a molecule of glycerol esterified to three molecules of fatty acids. Steps: