1. Chapter 10 Lipids

2. Characteristics  Water insolubility  Chemical diversity Biological functions  Energy storage; fats & oils  Components of biological membrane; phospholipids & sterols  Enzyme cofactors, electron carriers, light-absorbing pigments, molecular anchors, emulsifying agent, hormones, intracellular messengers 1. Storage lipids 2. Structural lipids 3. Biologically active lipids

3. 10.1 Storage Lipids “Cellular oxidation of fatty acids is highly exergonic”

4. Fatty Acids Fatty acids  Carboxylic acids with hydrocarbon chains  C 4 to C 36  Saturated or unsaturated (one or more double bonds)  A few contain C 3 ring, -OH, -CH 3 branches Nomenclature  Chain length: # of double bonds (  positions of double bonds )

6. Common Fatty Acids Even number of carbon atoms Common patterns of double bonds  Monounsaturated fatty acids:  9  Polyunsaturated fatty acids :  9,  12,  15  No conjugated patterns (separated by methylene group)  cis configuration of double bonds Trans fatty acids  Fermentation in the rumen of dairy animals  Partial hydrogenation of vegetable oils  Increase blood levels of LDL (bad cholesterol) and decrease HDL (good cholesterol)

7. Omega-3 & -6 PUFA Omega-3 PUFA  -linolenic acid  ALA; 18:3(  9,12,15 )  Essential PUFA in human ; synthesis of eicosapentaenoic acid (EPA; 20:5(  5,8,11,14,17 )) & docosahexaenoic acid (DHA; 22:6(  4,7,10,13,16,19 ))  Supply via the diet (rich in vegetable & fish oils)  Maintenance of the optimal dietary ratio of  -6 to  -3 PUFA  critical for health Omega-6 PUFA

8. Physical Properties of Fatty Acids Length & unsaturation degrees of hydrocarbon chain Water solubility  Longer chain  lower solubility  Polar carboxylic group  a little solubility Melting point  Depending on the degrees of packing  Saturated fatty acid ; tight packing (waxy or cystalline arrays)  high melting point  Unsaturated fatty acid ; loosely packing by kinks of cis double bond (oily liquid)  low melting point

9. Triacylglycerol (triglycerides, fats, neutral fats)  3 fatty acids each in ester linkage with a single glycerol  Simple triacylglycerols  Same 3 fatty acids  Tripalmitin (16:0), tristearin (18:0), triolein (18:1)  Mixed triacylglycerols (most natural triacylglycerols)  Nonpolar & hydrophobic

10. Triacylglycerol (triglycerides, fats, neutral fats) Function  Energy storage  Lipid droplets in cytosol  Adipocytes in vertebrate & seeds in plants  Lipase  hydrolysis of stored TAG & release of fatty acids  Advantages of TAG as stored fuels  High energy yield  No extra weight of water of hydration  Fat tissues; under the skin, in the abdominal cavity & mammary glands  Insulation against low temperature  Seals, penguins, hibernating animals  Dual functions of energy storage & insulation  Matching the buoyancy of the body  Sperm whale  Spermaceti oil in the head  Increase in density during cold deep sea diving

11. Triacylglycerols in Food Triacylglycerols in food  Vegetable oils  TAG with unsaturated fatty acids  Liquids at room temperature  Animal fats  High content of TAG with saturated fatty acids  Solids at room temperature Oxidation of fats in air  Oxidative cleavage of double bonds  Generation of aldehydes and carboxylic acids of shorter chain length  volatile  rancidity  Partial hydrogenation (cis double bonds  single bond)  increase shelf-life; margarine  harmful effect; formation of trans fatty acids

13. Waxes Structure  Esters of long-chain (C 14 to C 36 ) saturated and unsaturated fatty acids with long-chain (C 16 to C 30 ) alcohols Properties  High melting points (60 to 100 o C)  Water repellent  Firm consistency Functions  In plankton : energy storage  Water repellent  Protection of hair in vertebrates, feather in birds, and leaves in plants  Industrial applications  Lotions, ointments, polishes

14. 10.2 Structural Lipids in Membranes

15. Types of Membrane Lipid Amphipathic  Hydrophobic chain  Hydrophilic head  Phosphate: phospholipid  Oligosaccharide : glycolipids

16. Glycerophospholipids (Phosphoglycerides) Ester linkage to glycerol  Two fatty acids  C-1 : C 16 or C 18 saturated fatty acid  C-2: C 18 to C 20 unsaturated fatty acid  Highly polar or charged group via phosphodiester linkage Wide variety

17. Glycerophospholipids (Phosphoglycerides)

18. Ether-Linked Fatty Acids Ether lipids  One of the acyl chains has ether linkage  Plasmalogens  ~ 50% of phospholipids in heart tissue  Platelet-activating factor  Signal molecule released from basophils (leukocytes)  Aggregation of platelet  Release of serotonin (vasoconstrictor) from platelets  Regulation of inflammation & allergic response

19. Galactolipids and Sulfolipids Galactolipid  1 or 2 galactose to C-3 via glycosidic linkage  Localized in the thylakoid membranes of chloroplasts  70% to 80% of the total membrane lipids in vascular plants  Most abundant membrane lipids in the biosphere Sulfolipid  Slufonated glucose to C-3 via glycosidic linkage

20. Membrane Lipids of Archaebacteria Glycerol dialkyl glycerol tetraethers (GDGT)  Ether linkages  More resistant to hydrolysis at low pH and high temperature than ester bonds  Polar head at each end

21. Sphingolipids General structure  Spingosine : long-chain amino alcohol  One long-chain fatty acid (amide linkage to –NH 2 on C-2)  Polar head group ; glycosidic or phosphodiester linkage  Ceramide; structural parent of all sphingolipids

22. Sphingolipids 3 subclasses of sphingolipids (polar head group)  Sphingomyelins  Phosphocholine or phosphoethanolamine  Prominent in myelin sheath, the insulator of axons  Glycosphingolipids  Neutral glycolipids  Cerebrosides ; single sugar: Gal (neural tissue), Glc (non-neural tissue)  Globoside : Two or more sugars  Gangliosides  Oligosaccharides with one or more N- acetylneuraminic acid (sialic acid)  negatively charged ganglioside »GM: 1 sialic acid, GD: 2 sialic acid etc.

23. Sphingolipids

24. Sphingolipids for Biological Recognition Sphingolipids  Named after Sphinx because of their enigmatic functions Functions of sphingolipids  Largely undiscovered  Blood typing  Glycosphingolipid  Signal recognition  Gangliosides; concentrated in the outer surface of cells  Embryonic development  Induction of tumor

25. Degradation of Phospholipids and Sphingolipids Degradation in lysosome Phospholipids  Phospholipase  Phospholipase A, C, D  Lysophospholipase Gangliosides  Stepwise removal of sugar units  Ceramide as a final product

26. Sterols Structure  Sterol nucleus; 4 fused rings  Planar & rigid  3 with C 6 and 1 with C 5 Types  Cholesterol; Major sterol in animal  Amphipathic  polar head + nonpolar hydrocarbon body  Stigmasterol; In plant  Ergosterol; In fungi Functions  Membrane structure  Precursors  Steroid hormones  Bile acids: detergents in the intestine