Ch7-13 ans - Chapter 7 Carbohydrates and Glycobiology 2...

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Chapter 7 Carbohydrates and Glycobiology 2. Sugar Alcohols- (Ans) With reduction of the carbonyl oxygen to a hydroxyl group, the chemistry at C-1 and C-3 is the same; the glycerol molecule is not chiral. 5. A Taste of Honey (Ans) Straight-chain fructose can cyclize to yield either the pyranose or the furanose structure. Increasing the temperature shifts the equilibrium in the direction of the furanose form, reducing the sweetness of the monosaccharide. The higher the temperature, the less sweet is the fructose solution. 8. Manufacture of Liquid-Filled Chocolates (Ans) Prepare the core as a semi-solid slurry of sucrose and water. Add a small amount of sucrase, and quickly coat the semi-solid mixture with chocolate. After the chocolate coat has cooled and hardened, the sucrase will hydrolyze enough of the sucrose to reduce the viscosity of the mixture of glucose and fructose, converting it to a more nearly liquid consistency. 9. Anomers of Sucrose? (Ans) Unlike lactose, sucrose has no free anomeric carbon to undergo mutarotation. 10. Physical Properties of Cellulose and Glycogen (Ans) Native cellulose consists of glucose units linked by ( $ 1 ÷ 4) glycosidic bonds. The $ linkages force the polymer chain into an extended conformation (see Fig. 9-17). Parallel series of these extended chains can form intermolecular hydrogen bonds, thus aggregating into long, tough, insoluble fibers. Glycogen consists of glucose units linked by ( " 1 ÷ 4) glycosidic bonds. The " linkages cause bends in the chain and prevent the formation of long fibers. In addition, glycogen is highly branched and, because many of the glucose hydroxyl groups are exposed to water, is highly hydrated and therefore very water-soluble. It can be extracted as a dispersion in hot water. The physical properties of the two polymers are well suited to their biological roles. Cellulose serves as a structural material in plants, consistent with its side-by-side aggregation into tough insoluble fibers. Glycogen is a storage fuel in animals. The highly hydrated glycogen granules with their abundance of free, non-reducing ends can be rapidly hydrolyzed by glycogen phosphorylase to release glucose 1-phosphate. 11. Growth Rate of Bamboo (Ans) First calculate the growth per second: (.03 m/day) (24 h/day)(60 min/h)(60 s/min) = 3.47 x 10 -6 Given that each glucose residue is 0.45nm (0.45 x 10 -9 ) long, the number of residues added per second is (3.47 x 10 -6 m/s) (0.45 x 10 -9 m/residue) = 7,716 residues . 7,700 residues/s 12. Glycogen as Energy Storage: How Long Can a Game Bird Fly?
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(Ans) The average molecular weight of a glucose unit in glycogen is 160. The amount of usable glucose (as glycogen) in 1 g of tissue is (0.0035 g) (160 g/mol) = 2.19 x 10 -5 mol In 1 min, 120 μmol of glucose 1-phosphate is produced, so 120 μmol of glucose is hydrolyzed. Thus depletion of the glycogen would occur in (2.19 x 10 -5 mol)(60 s/min) (120 x 10 -6 mol/min) = 10.9 s . 11 s 13. Volume of Chondroitin Sulfate in Solution (Ans) The negative charges of chondroitin sulfate repel each other and force the molecule into an extended conformation. The polar molecule also attracts many water molecules (water of
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