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3.Lipids

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3.Lipids

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  1. Chapter 2 Lipids • Lipidsare heterogeneous group of compounds which are related more by their physical properties. • They are insoluble in water and soluble in non-polar organic solvents (alcohol, ether, benzene, chloroform and acetone) • Lipids are important because of their • high energy value • delivery of fat soluble vitamins • delivery of essential fatty acids found in foods. • The lipids include fatty acids, triglycerides,phospholipids, sphingolipids, sterols, waxes, glycolipidsand lipoproteins.

  2. Fatty Acids • Vary with respect to their size, and the numberand positionof double in the molecule • Classified by; • the number of carbon atoms as short chain (C4-6),medium chain (C8-12) and long chain (C12+) • Presence and absence of double bonds as unsaturated and saturated • Saturated fatty acids generally designated by the formula : CnH2n+1COOH. • The most common ones are: • lauric acid; CH3 (CH2)10 COOH • myristic acid; CH3 (CH2)12 COOH • palmitic acid ;CH3(CH2)14 COOH • stearic acid ;CH3(CH2)16 COOH

  3. The most common dietary monounsaturated fatty acid is oleic acid : CH3(CH2)7CH=CH(CH2)7COOH. • The polyunsaturated fatty acids contain two or more double bonds. Examples linoleic acid: CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH α-linolenic acid:CH3CH2CH=CHCH2CH=CHCH2CH=CH (CH2)7COOH (these are essential fatty acids as they cannotbe synthesized by your body and must be obtained from the diet) Arachidonic acid: CH3(CH2)4CH=CHCH2CH=CHCH2CH=CHCH2CH=CH(CH2)7COOH

  4. Unsaturated fatty acids also classified geometrically as Trans and cis fatty acids( geometrical isomers ) • Unlike trans one the cis isomers are more important bc their structure (high sterik hindrance)does not allow them to bind together and to solidify at room temperature, thus they are liquid at room T. • Trans and cis fatty acids trans cis

  5. Trans isomers are equivalent with saturated fats • They are hard to metabolize and excrete from the body(leads to greater heart disease) • Less effective as energy source e.g. Omega - 3 Fatty Acids • Refers to the position of the 1st double bond relative to the terminal CH3.( Omega = terminal) • These fatty acids are advertized as dietary supplement Examples: eicospentaenoic acid; EPA, docosahexaenoicacid ; DHA. • Dietary source : fish oil, flaxseed, safflower, sunflower and soybean oils, corn oil.

  6. Cont… Linoleic Acids (Omega 6) Eighteen-carbon essential fatty acids that contain two double bonds. 18:2 (9,12) • Linolenic Acids (Omega 3) • Eighteen-carbon essential fatty acids that contain three double bonds • 18:3 (9,12,15)

  7. 2. Triglycerides • They are esters of glycerol and fatty acids and can be represented by the formula: • Un like other animal fats human milk and Pork fat have unsaturated fatty acids in R2 and R3. • Vegetable oils generally have an unsaturated fatty acid (usually linoleicacid) at the R2 position with saturated fatty acids located at the R1 and R3 positions.

  8. 3.Phospholipids • A great variety of phospholipids is present in the body • They are found predominantly in animal tissues as a structural component of cell walls and mitochondria. In the blood, as a component of lipoproteins, • Phospholipids serve in the transport of fat between tissues. • The phospholipids(phosphoglycerides) may be represented by the general formula:

  9. 4.Sphingolipids • The sphingolipids are a class of lipids in which the glycerol is replaced by sphingosine or its derivative. • Sphingosine is both an alcohol, and a nitrogen containing base. CH3(CH2)12 CH=CHCH(OH)CH(NH2) CH2OH • Is an important constituent of the myelin sheath of nerves

  10. 5. Sterols • Sterols are alcohols containing the steroid structure of four fused carbon rings. • Cholesterol is the predominant sterol in higher mammals. It is present in all animal tissues but not in plants. Egg yolk, dairy products, shellfish and meats are examples.

  11. The bile salts (sodium glycocholate and sodium taurocholate) Estrogen, androgens, progesterone, and most of the adrenocortical hormones are derived from cholesterol. • Ergosterol (the derivative of cholesterol) is converted into vitamin D under the influence of ultraviolet light. 6. Waxes • Waxes are fatty acid esters of higher alcohols. • They occur widely in the cuticle of leaves and fruit and in the secretions of insects. • Waxes are not an important constituent of any of the higher land animals nor do they contribute extensively to normal human diets.

  12. Functions of Fats • Dietary fat is the most concentrated source of energy, supplying 9 kcal/g, (37 kJ/g). • Dietary fat acts as the source of fat-soluble vitamins and the essential fatty acids. • The essential fatty acids are required for; • growth, • reproduction, • skin integrity, • utilization of body fat and • maintenance of cell membranes.

  13. Digestion and Absorption • The majority of dietary fat is ingested in the form of triglycerides (90-95 percent) • Since lipids are insoluble in water they must be complexed with protein (lipoprotein) for transport in the lymph and blood. • Most absorbed dietary fat is transported in the form of lipoproteins. • The chylomicrons are released into the lymphatic system and ultimately enter the blood

  14. Transport of Lipids • The majority of plasma lipids are transported as lipoproteins. • The four main class of the lipoproteins are the chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) • Fat soluble vitamins and carotenoids, sterols and hormones are also transported in the blood in combination with specific plasma proteins.

  15. Chylomicrons • transport most of the dietary triglyceride from the intestine VLDL • Serve to transport endogenous triglycerides to extra hepatic tissues ( out of liver ) • Most VLDL remnants do not undergo hepatic uptake. Instead, they undergo a series of reactions forming intermediate density lipoproteins and ultimately low density lipoproteins (LDL)

  16. LDL • Serve to deliver cholesterol(over 2/3 ) from the liver to the extrahepatictissues. • LDL particles bind to a cell-surface receptor and enter the cell by endocytosis( cellular absorption) HDL • Are believed to deliver cholesterol from the peripheral tissues to the liver where it is catabolized and HDL cholesterol is eliminated via the biliary system. HDL or LDL? • LDL: “bad” • associated with high risk of heart attack • HDL: “good: • protective effect for heart

  17. Metabolism • Excess dietary triglycerides are stored mainly in adipose tissue. • They may be transported • When there is energy deficit triglycerides are mobilized and oxidized to form ATP. Dietary Fat and Cancer • High levels of dietary fat increase the risk of many types of cancer, especially colon, lung, ovary and prostate cancers

  18. Controlling LDL and HDL • lower LDL or raise HDL • weight control • unsaturated instead of saturated fat • fibers • phytochemicals • moderate alcohol consumption • physical activity Role of Lipids • provide energy • insulation • protection against shock • cell membrane structure • deficiencies • retarded growth, skin lesions, kidney and liver disorders

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