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Biochemistry - Outline ch. 9

Biochemistry - Outline ch. 9 - Biochem Outline Chapter 9...

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Biochem Outline – Chapter 9 Lipids have 3 biological functions: 1. Lipid bilayers - essential components of biological membranes 2. Lipids containing hydrocarbon chains serve as energy stores 3. Many intra- and inter- cellular signaling events involve lipid molecules Major Classes of Lipids 1. Fatty Acids a. Carboxylic acids with long-chain hydrocarbon side groups b. Fatty acids usually have between 14-20 carbon atoms (most have an even number) c. More than half are unsaturated (often polyunsaturated) d. 1 st double bond of unsaturated generally occurs at the C9-C10 (counting from the carboxyl carbon) e. Nutritional nomenclature = i.e. omega-3, omega-6. Identifies last double bonded carbon atom counting from the methyl terminal (omega end) f. Saturated fatty acids are highly flexible due to free bond rotation (steric hindrance mean straight is lowest energy conformation) g. Fatty acid double bonds almost always have cis putting a bend in the hydrocarbon chain, reducing London forces i. This means that the more unsaturated, the lower the melting point (easier to break chains when there are fewer London forces around) ii. However, fluidity (ability to undergo transition from viscous gel state [frozen] to fluid liquid-crystalline state [liquid] - evidenced most strongly in bilayers) increases the more unsaturated it gets (more double bonds mean easier shifting, easier to change the bilayer structure as London forces are weaker) 2. Triacylglycerols a. A.k.a. triglycerides b. Fatty acid tri-esters of glycerol c. Function as energy reservoirs in animals; most abundant class of lipids d. Plant oils usually richer in unsaturated fatty acids than animal fats (think about melting points, here, and fluidity – link concepts) e. Highly efficient energy storage i. Less oxidized, so yield more energy/unit when oxidized
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ii. Nonpolar and stored in anhydrous form f. Adipocytes (fat cells in animals) are specialized for synthesis and storage of triglycerides 3. Glycerophospholipids a. A.k.a. phosphoglycerides b. Major component of biological membranes c. Are glycerol-3-phosphate where C1 and C2 are esterified fatty acids (COOR), and phosphoryl group is usually linked to another polar group (X) d. When X=H, these are phosphatidic acids; present in tiny amounts in membranes e. Phospholipases catalyse hydrolytic reactions with glycerophospholipids f. Enzymes that act on lipids must gain access to the lipid areas that are buried in non-aqueous environments i. They are relatively small proteins ii. Enzyme may fit polar head group into active site, then interact the tail with aromatic side chains iii. Products so hydrolyzed are not always going to be hydrolyzed further – occasionally hydrolyzed glycerophospholipids will be intra- and extra-cellular signaling molecules g. Plasmalogens are glycerophospholipids in which the C1 is linked with a double bond in cis (COCHCHR as compared to COCOR) i. Plasmalogens are mysterious ii. Due to vinyl group being easily oxidized, they might react with oxygen free radicals, preventing free radical damage to other cells 4.
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