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LIPID

Lecture-5. LIPID. Fatty acids in food: saturated vs unsaturated. % Fatty Acids. Source Lauric/Myristic Palmitic Stearic Oleic Linoleic. Beef 5 26-32 20-25 37-43 2-3 Milk 25 12 33 3

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LIPID

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  1. Lecture-5 LIPID

  2. Fatty acids in food: saturated vs unsaturated % Fatty Acids Source Lauric/Myristic Palmitic Stearic Oleic Linoleic Beef 5 26-32 20-25 37-43 2-3 Milk 25 12 33 3 Coconut 74 10 2 7 Corn 8-12 3-4 19-24 34-62 Olive 9 2 84 4 Palm 39 4 40 8 Soybean 9 6 20 52 Sunflower 6 1 21 66

  3. Lecture 15. Lipids 3 Lipids • Lipids have low solubility in water; • Lipids are amphipathic (polar and nonpolar); • Lipids are a principle component of biological membranes; • highly reduced forms of carbon; yield large amount of energy upon oxidation in metabolism;

  4. Roles of Lipids • Structural elements(phospholipids, cholesterol) • Energy storage(fatty acids, triacylglycerols) • Hormones( sex hormones e.g. Estrogen, testosteron) • Enzyme cofactors(coenzyme A) • Electron carriers(coenzyme Q, plastpquinone) • Light-absorbing pigments(carotenoids) • Emulsifying agents(bile salts) • Intracellular messengers(phosphatidyl inositol)

  5. Head group Tail group Spontaneously Formed Lipid Structures • Hydrophobic interactions are important • Lipid is an amphipathic molecule, • but rarely exists as a monomer. air water monolayer Lipid bilayer Micelle

  6. What is soap ? TAG + 3KOH (NaOH)  3RCOO-K+ + glycerol • FA chains can dissolve in oils while charged carboxyl group dissolves in water; • Forms a mixed micelle which can remove oils; • Soap form precipitates with divalent cations (reduces efficiency); • Detergent (modified FAs) do not precipitate with calcium, used as better cleaning agents.

  7. Lipids and the Structure of the Plasma Membrane To minimize interactions of FA chains (non-poplar), phospholipids aggregates form a bilayer structure. glycolipid Polar head hydrophobic tail Integral protein cholesterol

  8. Fatty Acids as Stored Energy • Fatty acids are the body’s principal form of stored energy • Carbon almost completely reduced as CH2 • Principal sources: dairy products, meats: Triacylglycerols, phospholipids, sterol esters

  9. Fatty acids (FAs) Structure andnomenclature • Basic formula: CH3(CH2)nCOOH • Carboxylic acids with hydrocarbon chains of 4-24 carbons • Free FAs are found in trace quantities in cells • FAs are either: • (i) part of a lipid molecule • (ii) complexed to a carrier protein • (e.g. albumin on blood) • Saturated or unsaturated

  10. Common Fatty Acids • Saturated fatty acids: • Lauric acid 12:0 • Myristic acid 14:0 • Palmitic acid 16:0 • Stearic acid 18:0 • Unsaturated fatty acids: • Palmitoleic acid 16:1 • Oleic acid 18:1 • Linoleic acid 18:2 • A-linoleic acid 18:3 (9,12,15) • G-linoleic acid 18:3 (6,9,12)

  11. Some Naturally Occurring Fatty Acids Chapter 15

  12. Naming of fatty acids C18    10 9 CH3-(CH2)7-CH=CH-CH2-CH2-CH2-CH2-CH2-CH2-CH2-COOH Cis 9 18:0, stearic acid : octadecanoic acid 18:1 (9), oleic acid : octadecenoic acid 18:2 (9,12), linoleic acid : octadecadienoic acid 18:3 (9,12,15), -linolenic acid : octadecatrienoic acid

  13. Lecture 15. Lipids 13 Triglycerols (triglycerides) • Triglycerols consist of a glycerol esterified with three fatty acids • If all fatty acid chains are the same, the molecule is called triacylglycerol (e.g., tristearin)

  14. Fats are largest subgroup of lipids • Made up of fatty acids and glycerol Chapter 15

  15. Naturally occurring fatty acids There is a common pattern in the location of double bonds: Unsaturated FA: 9, 12, 15 ……… Polyunsaturated FA: double bonds are never conjugated and are seperated by–CH2(-CH=CH-CH2-CH=CH-)n

  16. Saturated b. Unsaturated

  17. Lecture 15. Lipids 17 Structural Consequences of Unsaturation • Saturated chains pack tightly and form more rigid, organized aggregates (i.e., membranes); • Unsaturated chains bend and pack in a less ordered way, with greater potential for motion.

  18. Saturated vs. Unsaturated Fats • Saturated fats have no C=C bonds • Saturated with hydrogen • Unsaturated fats have C=C bonds • May have more than one double bond • Can add more hydrogen to fats • React readily with iodine, bromine, and chlorine Chapter 15

  19. Iodine Number • Iodine Number: number of grams of iodine consumed by 100 g of fat Chapter 15

  20. Waxes - Esters of long chain fatty acids • (C14-36) with long chain • (C16-30) alcohols • - High melting points (60-100C) • Energy storage • (Plankton, 浮游生物) • Water repellant • (birds and plants)

  21. Phospholipids 2 Classes of phospholipids (PL) (i) glycerolphospholipids – glycerol backbone (ii) sphingomyelin – spingosine backbone Glycerolphospholipids - essential for membrane structure - most abundant membrane lipids Sphingolipids - Component of a certain membrane - Sphingosine, fatty acid and glycoside

  22. L-Glycerol-3-phosphate, the backbone of phospholipids

  23. Lecture 15. Lipids 25 Fatty acid moiety Examples of Phosphatides O C H O 2 Phosphatidylcholine O CH O CH O 3 Fatty acid moiety C ) H N (CH O CH O P 3 2 2 2 CH O 3 Fatty acid moiety Phosphatidylethanolamine N ) H (CH 3 2 2 Phosphatidylserine COO CH C H O 3 NH 3

  24. Lecture 15. Lipids 26 Sphingolipids • Sphingosine forms the backbone of sphingolipids (rather than glycerol); • Sphingosines are important components of biological membranes; • Ceramide = sphingosine + fatty acid (via an amide linkage); • Sphingomyelins = ceramide + phospholipids (via 1-hydroxyl group) • Glycosphingolipids = ceramide + b-linked sugar at the 1-hydroxyl moiety.

  25. Sphingolipids

  26. Lecture 15. Lipids 28 Examples of Sphingolipids Ceramide Sphingosine C O H 3 H O CH O P O CH N CH H OH OH 2 H OH OH 2 2 3 H H H O CH C OH C CH C H 3 C CH 2 2 C C CH H NH 2 H NH 3 H H Cholin NH H O H Sphingomyelin O R-COOH R fatty acid R

  27. Similarities between phosphatidylcholine and sphingomelin

  28. Lecture 15. Lipids 30 Terpenes • Terpenes are a class of lipids from two or more molecules of 2-methyl-1,2-butadiene, or isoprene; • Example of a terpene molecule: • All sterols (including cholesterol) and steroid hormones are terpene-based molecules

  29. Cholesterol • Steroids: • (i) cholesterol and sterols of plants and fungi • (ii) steroid hormones • (iii) bile salts • Roles of cholesterol in mammals • (i) structural component of plasma membrane and • modulates membrane fluidity • (ii) precursor of steroid hormones and bile acids • Rarely found in plants, never in bacteria

  30. Lecture 15. Lipids 32 Steroids • Based on a core structure consisting of three 6-membered rings and one 5-membered ring, all fused together; • Cholesterol is the most common steroid in animals and precursor for all other steroids in animals; • Steroid hormones serve many functions in animals - including salt balance, metabolic function and sexual function;

  31. Lecture 15. Lipids 33 Steroid Examples OH C D H C 3 C D CH CH 3 A B CH A 2 B O CH 2 testosterone CH synthesized in five Cyclopentanoperhydrophenanthrene 2 steps from cholesterol CH CH 3 CH OH 2 H C C D 3 C D A B A B HO HO Cholesterol Estradiol

  32. Cholesterol

  33. Steroid hormones carry messages between tissues • Derivates of sterols; • Sex hormones and hormones from adrenal cortex; • Play important roles in gene expression; • Prednisolone and prednisone are steroid drug with potent antiinflammatory activities.

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