Transportation .. Metabolism LIPIDS Digestion .. Absorption .. Transportation .. Metabolism Dina Trabzuni

Lipids consist of two parts Glycerol Fatty Acids a. Saturated fatty acids b. Unsaturated fatty acids .Monounsaturated . Polyunsaturated Figure 3 : Formation of TG

Table 1 : Saturated fatty acids

Table 2 : Unsaturated fatty acids

Lipids are classified as simple or complex Simple lipid a. Fatty acids b. neutral fats (monoglyceride, diglycerde, and triglyceride) c. waxes Complex lipids a. Phospholipids b. Glycolipids c. Lipoproteins 3. Derived lipids Figure 1 : Triglyceride Figure 2 : Phosphatidic acid

Omega Fatty acid

Cis- Trans Fatty acid

. Flavor and Satisfaction Function of Fat . Energy . Essential nutrient . Flavor and Satisfaction . Adipose Tissue . Cell membrane Structure Fat in Food Fat in Body

. Meat Fat (bacon, sausage….) Food Sources of Fat . Meat Fat (bacon, sausage….) . Dairy Fats and products (cream, butter, cheese..) . Egg yolk . Monounsaturated , polyunsaturated Fatty acid . Vegetable oil (safflower, corn, soybean, cottonseed, olive oil) Animal Fats Plant Fat

. Butter, margarin, salad oils and dressing,shirteninig fat meat Characteristics Of Food Fat Sources . Butter, margarin, salad oils and dressing,shirteninig fat meat . Chees, cream portion of homogenised milk, egg yolk, nuts, seeds, olives….. Visible Fat Invisible Fat

Digestion of lipids In mouth mechanical digestion Lingual Lipase In stomach mechanical digestion Gastric lipase

Bile acid, Pancreatic Lipase, Cholesterol esterase, Phospholipase In small intestine Bile acid, Pancreatic Lipase, Cholesterol esterase, Phospholipase Triglycerides 2 fatty acids + Mono glycerides 3 fatty acids + glycerol Pancreatic lipase 1 fatty acids + Diglycerides

Absorption of lipids Figure 4 : Absorption of fat.

Transportation of lipids Table 3 Lipids are transported in the plasma as lipoproteins. Source Destination Major lipids Functions Chylomicrons Intestine Many organs Triglycerides, other lipids Deliver lipids of dietary origin to body cell. VLDLs Liver Triglycerides, Cholesterol Deliver endogenously produced triglycerides to body cells. LDLs Intraviscular removal of triglycerides from VLDL Blood vessels, Liver Cholesterol Deliver endogenously produced cholesterol to various organs. HDLs Liver and intestine Liver and steroid-hormone-producing glands Remove and degrade Cholesterol.

. Adipose tissue is the main store of triglyceride in the body. Lipids Metabolism . Liver and Adipose tissue play a central role in lipid metabolism. . Adipose tissue is the main store of triglyceride in the body. . Lipid metabolism either lipolysis or lipogenesis. . Fatty acids are both oxidized to acetyl CoA and synthesized from acetyl CoA.

Lipolysis . Complete hydorlysis of triglyceride yeild gelycerol and 3 fatty acids. . Fatty acids oxidiation take place in the mitochonderia. . Fatty acids are activated before being catabolized (oxidized). Fatty acid + ATP + CoA Acyl CoA + AMP + PPi acyl CoA synthetase

Long chain fatty acids penetrate the inner -Mitochinderial membrane as carnitine derivatives. Figure 5 : Role of carnitine in the transport of long chain fatty acids.

β - oxidation pathway of fatty acids . Many tissues are capable of oxidizing fatty acids in the mitochondria by β - oxidation pathway. . The chain is broken between the α (2) and β (3) carbon atoms. Figure 6 : Overview of β - oxidation pathway of fatty acids

β - oxidation of fatty acids (Figure 7)

The products of oxidation of fatty acids Oxidation of fatty acids produces a large quantity of ATP, .example : Palmitic acid (C:16 ) 7 cycles from 7 NADH + 7 FADH2 (7 x5 = 35 ATP) 7 cycles from 8 Acetyl CoA (8 x 12 = 96 ATP) 2 ATP for the initial activation of fatty acid ( 35 +96 – 2 = 129 molecule of ATP) Figure 8 : acetyl CoA product

Oxidation of unsaturated fatty acids occurs by amodified β - oxidation pathway (figure9)

Ketone bodies Ketogenesis occurs when there is a high rate of fatty acid oxidation in the Liver (figure 10). Acetyl CoA Acetyl CoA CoA Aceto acetyl CoA CoA Acetoacetate β -hydroxy butyrate Acetone

Lipogenesis . The body is capable of synthesizing fatty acids in the cytoplast of the cell from starter ( acetyl CoA + malonyl CoA). . Malonyl CoA is formed from Acetyl CoA Figure 11 : Biosynthesis of Malonyl CoA

. Acetyl CoA transfer to the cytoplast across the mitochondrial membrane in the form of citrate Figure 12 : Conversion the citrate to Oxaloacetate and Acetyl CoA. . The enzymes involved in fatty acid synthesis are arranged in a complex called the fatty acid synthase system.

The steps in the synthesis of fatty acid ( Figure 13)

. Cholesterol is not an energy producing nutrient. . It is an essential structural component of membrane of the outer layer of plasma lipoprotien. Bile acids and steriod hormones are formed from cholesterol. . Cholesteryl ester is a storage form of cholesterol which is found in most tissues. Figure 14 : Cholesterol

Acetyl CoA is the source of all carbon atoms in cholesterol Acetoacetyl CoA CoA Acetyl CoA Inhibition β -hydroxy- β- methylglutaryl CoA HMG-CoA reductase Mevalonate Squalene Cyclization Farmesyl pyrophosphate

References Brene, R., Levy, M., Koeppen, B., Stanton, B., (2004) Physiology, Fifth edition. Mosby.   Fox, S., (2004) Human Physiology, Eighth edition. Mc Graw Hill. Hunt, S., Groff, J., (1997) Advanced Nutrition and Human Metabolism, West Puplishing Company. Lehninger, A., Nelson, D., Cox, M.,(1993) Principles of Biochemistry, 2nd edtion. Worth Puplishers. Murray, R., Granner, D., Mayes, P., Rodwell, V., (1996) Haper’s Biochemistry, 24th edition, Prentic-Hall International, Inc. Seeley, R., Stephens, T., Tate, P., (1992) Anatomy and Physiology,Mosby Yearbook.

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