答:C 13. A membrane-affiliated protein is isolated by detergent extraction, and found to be amphipathic and lacking any nonprotein components. To which class of membrane proteins does it belong? integral proteins b. peripheral proteins c. lipid-anchored proteins d. none of the above 答:a 14. The distribution of kt across an artificial membrane was measured and the concentrations were found to be equal on both sides. Which of the following statements is true about the distribution of K? a. K must be at equilibrium across the cell membrane b. K cannot be at equilibrium across the membrane c. There cannot be a membrane potential under these cond itions d. more information is needed to determine whether K+ is at equilibrium 答:d 15. Which of the following is not a step in the regulation of glycogen metabolism a Epinephrine stimulates an increase in cAMP. b A cAMP-dependent kinase phosphorylates glycogen phosphoryl c A CAMP-dependent kinase phosphorylates glycogen d A rise in cAMP activates a cAMP-dependent protein kinase 答b 16. Both rine and glucagon bind to C protein-oupled receptors an activate glycogen breakdown. Therefore, epinephrine and glucagon must a. have very similar structures and bind to the same receptor b bind to receptors with different ligand- bind ing sites but similar c. bind to different receptors and activate different second messengers d bind to the same receptors, one being intracellular and the other extracellular 答b 17. Which mutant form of ras is likely to cause malignancy?7 答: c 13. A membrane-affiliated protein is isolated by detergent extraction, and found to be amphipathic and lacking any nonprotein components. To which class of membrane proteins does it belong? a. integral proteins b. peripheral proteins c. lipid-anchored proteins d. none of the above 答:a 14. The distribution of K+ across an artificial membrane was measured, and the concentrations were found to be equal on both sides. Which of the following statements is true about the distribution of K+? a. K+ must be at equilibrium across the cell membrane. b. K+ cannot be at equilibrium across the membrane. c. There cannot be a membrane potential under these conditions. d. More information is needed to determine whether K+ is at equilibrium. 答:d 15. Which of the following is not a step in the regulation of glycogen metabolism: a. Epinephrine stimulates an increase in cAMP. b. A cAMP-dependent kinase phosphorylates glycogen phosphorylase. c. A cAMP-dependent kinase phosphorylates glycogen phosphorylase kinase. d. A rise in cAMP activates a cAMP-dependent protein kinase. 答:b 16. Both epinephrine and glucagon bind to C protein~oupled receptors and activate glycogen breakdown. Therefore, epinephrine and glucagon must: a. have very similar structures and bind to the same receptor. b. bind to receptors with different ligand-binding sites but similar functions. c. bind to different receptors and activate different second messengers. d. bind to the same receptors, one being intracellular and the other, extracellular. 答:b 17. Which mutant form of ras is likely to cause malignancy?