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Section VIII – Biochemistry of Extracellular & Intracellular Communication

Regarding membrane lipids, select the one FALSE answer.

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

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

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

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

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

Glycolipids are located on the outer leaflet.

Regarding membrane proteins, select the one FALSE answer.

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

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

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

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

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

Alpha-helices are major constituents of membrane proteins.

Regarding membrane transport, select the one FALSE statement.

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

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

C. Facilitated diffusion requires a protein transporter.

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

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

Insulin also increases glucose uptake in muscle.

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

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

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

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

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