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18.4 Chemical properties of fats and oils
1. Hydrolysis– Reverse of esterification– Forms carboxylic acids (FAs) and alcohol (glycerol)– Catalyst = acid or enzyme (lipase)
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Chemical reactions of TAGs
2. Saponification (hydrolysis in base)– Forms carboxylic acid salts (soaps)– Na+ = hard soap; K+ = liquid soap
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Chemical reactions of TAGs
3. Hydrogenation– Unsaturated chains add H2 (become “hydrogenated”)
– Increase the melting point (become semi-solid)
– Side effect = production of trans fats
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Olestra
• Artificial, noncaloric fat substitute (indigestible)
• FDA warning– “This Product Contains Olestra. Olestra may cause abdominal
cramping and loose stools. Olestra inhibits the absorption of some vitamins and other nutrients. Vitamins A, D, E, and K have been added.”
Reaction map for triglycerides
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18.5 Waxes
• Esters of fatty acids• Alcohol has long chain• Insoluble in water• Not easily hydrolyzed• Natural protective
coatings on plants, fruit, skin, fur, feathers
• Commercially used as candles, cosmetics
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Membrane/structural lipids
• 18.6 Phospholipids (phosphoglycerides)• 18.7 Sphingolipids (sphingomyelins and glycolipids)
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18.8 Biological membranes
• Separate contents of cells from external fluids• Semipermeable
– Nutrients enter, waste products leave
• Lipid bilayer = structural lipids and cholesterol
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Fluid-mosaic model
• Ex: Cholesterol, hormones• 4 ring structure
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18.9 Steroids
• Contains –OH• Produced by liver• Supplied by diet• Precursor for hormones, vitamin D• Component of cell membranes
– Provide rigidity
• High levels– Gallstones– Deposits on arteries
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Cholesterol
• Chemical messengers carried through the blood
• Same 4-ring structure as cholesterol
• Examples:– Cortisol: increase glucose
concentration in the body– Cortisone: anti-inflammatory
(arthritis, asthma)– Testosterone, estradiol,
estrone, progesterone: sex hormones
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18.10 Steroid hormones
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18.11 Prostaglandins
• Hormones involved in production of pain, fever, inflammatory reactions
• Synthesized from arachidonic acid (a polyunsaturated FA)• Synthesis inhibited by NSAIDs
– e.g. acetylsalicylic acid (aspirin)
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Summary of lipids