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Section VIII: Biochemistry of Extracellular & Intracellular Communication

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Regarding membrane lipids, select the one FALSE answer.

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A. The major phospholipid by mass in human membranes is generally phosphatidylcholine.

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B. Glycolipids are located on the inner and outer leaflets of the plasma membrane.

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C. Phosphatidic acid is a precursor of phosphatidylserine, but not of sphingomyelin.

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D. Phosphatidylcholine and phosphatidylethanolamine are located primarily on the outer leaflet of the plasma membrane.

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E. The flip-flop of phospholipids in membranes is very slow.

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B. Glycolipids are located on the outer leaflet.

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Regarding membrane proteins, select the one FALSE answer.

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A. Because of steric considerations, alpha-helices cannot exist in membranes.

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B. A hydropathy plot helps one to estimate whether a segment of a protein is predominantly hydrophobic or hydrophilic.

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C. Certain proteins are anchored to the outer leaflet of plasma membranes via glycophosphatidylinositol (GPI) structures.

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D. Adenylyl cyclase is a marker enzyme for the plasma membrane.

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E. Myelin has a very high content of lipid compared with protein.

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A. Alpha-helices are major constituents of membrane proteins.

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Regarding membrane transport, select the one FALSE statement.

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A. Potassium has a lower charge density than sodium and tends to move more quickly through membranes than does sodium.

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B. The flow of ions through ion channels is an example of passive transport.

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C. Facilitated diffusion requires a protein transporter.

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D. Inhibition of the Na+-K+-ATPase will inhibit sodium-dependent uptake of glucose in intestinal cells.

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E. Insulin, by recruiting glucose transporters to the plasma membrane, increases uptake of glucose in fat cells but not in muscle.

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E. Insulin also increases glucose uptake in muscle.

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Regarding the Na+-K+-ATPase, select the one FALSE statement.

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A. Its action maintains the high intracellular concentration of sodium compared with potassium.

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B. It can use as much as 30% of the total ATP expenditure of a cell.

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C. It is inhibited by digitalis, a drug that is useful in certain cardiac conditions.

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