Fundamentals of biochemistry 4th edition voet test bank

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Chapter 10: Membrane Transport Matching A) Porins B) gap junctions C) symport D) active E) ion channel F) secondary active G) channel-forming H) carrier ionophores I) passive-mediated J) uniport K) simple diffusion L) anti-ion transport

1. ______ are transporters that bind the substance to be transported on one side of the membrane then diffuse through the membrane and release the substance on the other side.

Ans: H Level of Difficulty: Easy Section: 10.2.A Learning objective: Passive-Mediated Transport

2. An example of nonmediated transport is ______.

Ans: K Level of Difficulty: Easy Section: 10.1 Learning objective: Thermodynamics of Transport

3. The GLUT1 transporter functions via _____ transport.

Ans: I Level of Difficulty: Easy Section: 10.2.E Learning objective: Passive-Mediated Transport

4. ______ are bacterial proteins forming a  barrel structure with a central aqueous channel.

Ans: A Level of Difficulty: Easy Section: 10.2.B Learning objective: Passive-Mediated Transport

5. Connexin proteins make up the structure of ______.

Ans: B Level of Difficulty: Easy Section: 10.2.E Learning objective: Passive-Mediated Transport

6. A transporter that moves two substances simultaneously in the same direction is an example of a(n) __________.

Ans: C Level of Difficulty: Easy Section: 10.2.E Learning objective: Passive-Mediated Transport

7. KcsA is an example of a ______ ionophore.

Ans: G Level of Difficulty: Easy Section: 10.2.C Learning objective: Passive-Mediated Transport 8. The Ca2+–ATPase requires ATP directly and is therefore an example of ______ transport.

Ans: D Level of Difficulty: Easy Section: 10.3.B Learning objective: Active Transport

9. The Na+–glucose transport system requires generation of a gradient by another transporter and is therefore an example of ______ transport.

Ans: F Level of Difficulty: Easy Section: 10.3.D Learning objective: Active Transport

10. KcsA is an example of a(n) _________.

Ans: E Level of Difficulty: Easy Section: 10.2.C Learning objective: Passive-Mediated Transport

Multiple Choice 11. Which of the following compounds would cross a biological membrane most readily by nonmediated diffusion?

A) water B) acetone C) hexane D) acetic acid E) methanol Ans: C Level of Difficulty: Easy Section: 10.1 Learning objective: Thermodynamics of Transport

12. Which of the following is an example of nonmediated transport?

A) simple diffusion B) facilitated diffusion C) passive transport D) active transport E) all of the above Ans: A Level of Difficulty: Easy Section: 10.1 Learning objective: Thermodynamics of Transport

13. Which statement does not describe the transport of ions by valinomycin?

A) Mutations in the peptide sequence may alter ability to transport through the membrane.

B) Transport may be active or passive.

C) The active site binds K+ with greater affinity than Na+ D) Transport results in equilibration of a concentration gradient across membranes.

E) All of the above do describe transport by valinomycin.

Ans: B Level of Difficulty: Moderate Section: 10.2.A Learning objective: Passive-Mediated Transport

14. Which of the following statements is true regarding ion channels?

A) Protein structure studies indicate a flexible pore size capable of transporting ions of varying size.

B) Ions require waters of hydration for sufficient passage through the entire channel.

C) Ion channels maintain sodium and potassium ion concentrations that are greater in the extracellular fluid than in the cytosol.

D) Channel rigidity minimizes energy states for appropriately sized ions.

E) None of the above is true regarding ion channels.

Ans: D Level of Difficulty: Difficult Section: 10.2.C Learning objective: Passive-Mediated Transport

15. Which of the following channels open in response to an extracellular stimulus such as a neurotransmitter?

A) mechanoselective channels B) ligand-gated channels C) signal-gated channels D) voltage-gated channels E) All of these are sensitive to an extracellular stimulus..

Ans: B Level of Difficulty: Easy Section: 10.2.C Learning objective: Passive-Mediated Transport

16. D-Glucose and D-mannitol are similarly soluble, but D-glucose is transported through the erythrocyte membrane four times as rapidly as D-mannitol. What is the most likely explanation?

A) D-glucose undergoes simple diffusion more rapidly than mannitol because glucose is less polar.

B) D-glucose and D-mannitol enter the erythrocyte via an ion-gated channel.

C) D-glucose and D-mannitol are transported via a system that distinguishes the two sugars.

D) D-glucose flux through the membrane is linear whereas D-mannitol flux is described by a hyperbolic curve.

E) None of the above provides the explanation.

Ans: C Level of Difficulty: Easy Section: Box 10.2 and 10.2E Learning objective: Passive-Mediated Transport

17. D-glucose is added to cells and the rate of glucose transport is plotted against D-glucose concentration. In the presence of the D-galactose derivative 6-O-benzyl-D-galactose, the curve is shifted to the right, indicating that D-glucose and the D-galactose derivative both compete for a place in the binding site. Which of the following is true?

A) The D-galactose derivative occupies some of the available binding sites.

B) Given the same concentration of glucose available, the number of binding sites with Dglucose present would decrease.

C) Given the same concentration of glucose, the rate of D-glucose flux would remain the same with the D-galactose derivative added.

D) Presumably a higher concentration of D-glucose would be required in order to maintain the same rate of D-glucose flux as before the D-galactose derivative was added.

E) All of the above are true.

Ans: E Level of Difficulty: Difficult Section: Box 10.2 and 10.2 E Learning objective: Passive-Mediated Transport

18. Which of the following is not an example of a passive-mediated transporter?

A) aquaporins B) the Kv ion channel C) GLUT1 D) lactose permease E) none of the above Ans: D Level of Difficulty: Easy Section: 10.2 Learning objective: Passive-Mediated Transport 19. Which of the following is (are) characteristic of the (Na+–K+)–ATPase?

I. It binds Na+ and K+ simultaneously prior to binding ATP II. It is covalently modified by phosphorylation at an Asp residue when Na+ is present.

III. Transport of Na+ and K+ occur in a 1:1 ratio, thus maintaining a balanced gradient until opening of the gated portion of the channel.

IV It is essential for excitation of nerve cells.

A) I, II, IV B) II, III, IV C) II, IV D) II, III E) II Ans: C Level of Difficulty: Difficult Section: 10.3.D Learning objective: Active Transport

20. Which of the transporters listed below differs from the others?

A) (Na+–K+)–ATPase B) Na+–glucose transporter C) lactose permease D) KcsA E) Ca2+–ATPase Ans: D Level of Difficulty: Easy Section: 10.3 Learning objective: Active Transport

21. When the cardiac glycoside, digitoxin, is used for heart failure, the effects include: I. inhibition of phosphate hydrolysis from E2 of the (Na+–K+)–ATPase pump II. activation of the (Na+–K+)–ATPase pump III. increase in intracellular Na+ concentration IV. increase in Ca2+ concentration in the sarcoplasmic reticulum A) I, II, III, IV B) I, III, IV C) II, III, IV D) II, III E) I, III Ans: B Level of Difficulty: Difficult Section: 10.3.A Learning objective: Active Transport

22. Which features allow the KcsA channel to selectively transport K+?

I. The entrance of the channel contains hydrophobic residues which forces the removal of waters of hydration.

II. It is attracted to the entrance of the channel via electrostatic interactions.

III. The “selectivity filter” involves a narrowing of the channel, allowing only dehydrated K+ access.

IV. As K+ is transported through the channel it interacts with −C=O groups from the protein.

A) I, II, III, IV B) II, III, IV C) II, III D) III, IV E) I, III Ans: B Level of Difficulty: Difficult Section: 10.2.C Learning objective: Passive-Mediated Transport 23. Gated ion channels I. exist because active transporters cannot maintain the gradient at a rate equal to nongated ion flow.

II. remain open unless acted on by an external stimulus.

III. remain open to all ions that are smaller than the pore diameter.

IV. can transport varying ions.

A) I, II B) I, III C) II, III D) II, IV E) I Ans: E Level of Difficulty: Difficult Section: 10.2.C Learning objective: Passive-Mediated Transport

24. Which does not occur when neurons are stimulated?

A) Local depolarization results from the opening of Na+ ion channels allowing Na+ to exit the cell.

B) Neighboring Na+ ion channels open in response to the change in membrane potential, resulting in a wave of depolarization.

C) Depolarization stimulates the opening of ion-gated K+ channels, resulting in repolarization .

D) Recovery involves the movement of Na+ out of the cell and K+ into the cell, resulting in the membrane regaining its resting potential.

E) All of the above do occur when neuron are stimulated.

Ans: A Level of Difficulty: Moderate Section: 10.2.C Learning objective: Passive-Mediated Transport

25. Vanilomycin A) is a cyclic polypeptide that functions as a K+ carrier.

B) is a transmembrane polypeptide that transports K+.

C) is a cyclic polypeptide that functions as a Na+ carrier.

D) is a transmembrane polypeptide that transports Na+.

E) is a -barrel pore transporter that transfers K+.

Ans: A Level of Difficulty: Easy Section: 10.2.C Learning objective: Passive-Mediated Transport 26. ClC Cl– channels I. assist in transport by forming a strong electrical dipole with the N-terminal end positively charged.

II. effectively funnel ions into the pore via electrostatic interactions with basic amino acids.

III. have a selectivity filter constructed from the N-terminal ends of α-helices, whose dipoles attract Cl– ions.

IV. rely on the side chain hydroxyl groups from Ser and Tyr. A) I, II, II, IV B) I, II, IV C) II, II, IV D) III, IV E) I, IV

Ans: A Level of Difficulty: Difficult Section: 10.2.C Learning objective: Passive-Mediated Transport

27. Which statement about aquaporins is false?

A) They transport water and hydronium ions efficiently.

B) They exclusively transport water molecules at a high rate.

C) They use hydrogen bonding to side chain NH2 groups of two Asn residues to exclude proton transport within the pore.

D) They have a narrow constriction approximately equal to the van der Waals diameter of a water molecule.

E) They use Arg and His side chains to remove associated water molecules from the ‘transported’ H2O. Ans: A Level of Difficulty: Moderate Section: 10.2.D Learning objective: Passive-Mediated Transport

28. Which of the following correctly rank the steps in erythrocyte glucose transport by GLUT1?

I. Glucose binding results in a conformational change, opening the binding site on the opposite side of the membrane II. Glucose binds to the transporter on one side of the membrane III. The transporter reverts to initial conformation IV. The glucose disassociates A) II, I, III, IV B) II, I, IV, III C) IV, III, II, I D) I, II, IV, III E) IV, II, III, I Ans: B Level of Difficulty: Moderate Section: 10.2.E Learning objective: Passive-Mediated Transport

29. Which of the following is true about the (Na+–K+)–ATPase transporter?

A) Three potassium ions bind to the cytostolic face of the transporter in the E1 state.

B) GTP binds to it and is hydrolyzed to form GDP and a high energy phosphorylated glutamyl residue.

C) Formation of the high-energy phosphorylated glutamyl residue triggers a conformational shift from the E1 form to the E2 form.

D) Phosphate hydrolysis of the E2 state releases potassium ions to the cytosol and results in rearrangement to the E1 state.

E) All of the above correctly describe this transporter.

Ans: D Level of Difficulty: Difficult Section: 10.3.A Learning objective: Active Transport 30. Ouabain inhibits the (Na+–K+)–ATPase pump, resulting in A) K+ ions moving into the cell along a concentration gradient B) K+ ions bringing water molecules into the cell in order to maintain an osmotic balance C) extra K+ ions and water in cells causing them to swell and lyse D) an increase in the strength of heart muscle contractions when small amounts of Ouabain are used E) all of the above Ans: D Level of Difficulty: Easy Section: 10.3.A Learning objective: Active Transport

31. Lactose permease uses a ___________ gradient generated ______ to cotransport lactose across the cell membrane.

A) potassium; via the Na+/K+ pump B) potassium; via oxidative metabolism C) proton; via the Na+/K+ pump D) proton; via oxidative metabolism E) chloride; within the intestinal lumen Ans: D Level of Difficulty: Moderate Section: 10.3.D Learning objective: Active Transport

32. The Kv channel is transiently closed by ___________.

A) a spherical globular segment on the N-terminus B) a C-terminal segment activated by proteolysis C) proteoglycan residues D) an ion larger than the selectivity filter blocking entry E) tightly-bound Ca2+ Ans: A Level of Difficulty: Moderate Section: 10.2.C Learning objective: Passive-Mediated Transport

33. A graph of the rate of glucose transport via the GLUT1 transporter vs. glucose concentration would have a ________ shape indicating that higher glucose concentrations increase the rate of transport until all the sites are saturated.

A) hyperbolic B) sigmoidal C) bell D) linear E) exponential Ans: A Level of Difficulty: Easy Section: 10.2.E Learning objective: Passive-Mediated Transport

34. In the intestinal epithelium, glucose enters the cell in symport with ______, which is subsequently ejected by ________.

A) K+; the Na+/K+ pump B) H+; oxidative metabolism C) Na+; the Na+/K+ pump D) Na+; the GLUT1 transporter E) Cl–; MDR transporter Ans: C Level of Difficulty: Moderate Section: 10.3.D Learning objective: Active Transport

35. The concentration of cytosolic Ca2+ is _________ the extracellular concentration of Ca2+.

A) dependent upon B) equal to C) 4 orders of magnitude greater than D) 2 order of magnitude greater than E) much less than Ans: E Level of Difficulty: Easy Section: 10.3.B Learning objective: Active Transport 36. Drug resistance is frequently traced to I. the MDR transporter.

II. overexpression of P-glycoprotein.

III. increased number of specific ABC transporters.

IV. the evolution of selectivity filters.

A) I, II, III B) II, III C) I, III D) III, IV E) II, IV Ans: A Level of Difficulty: Moderate Section: 10.3.C Learning objective: Active Transport

37. A pore that simultaneously transports two different molecules in different directions is called A) a symport.

B) a uniport .

C) a gap junction.

D) an equilibrium channel.

E) an antiport.

Ans: E Level of Difficulty: Easy Section: 10.2.E Learning objective: Passive-Mediated Transport

38. Gap junctions A) connect the cytoplasm to the extracellular solution thus allowing transfer of small molecules out of the cell into the extracellular solution.

B) are essential communication channels between the cell and the extracellular solution.

C) allow exchange of small molecules between cells within an organ.

D) allow intercellular exchange of macromolecules.

E) All of the above.

Ans: C Level of Difficulty: Difficult Section: 10.2.E and Box 10-1 Learning objective: Passive-Mediated Transport 39. The rapid transport of K+ ions by the KcsA ion channel moves up to ____ ions per ______.

A) 106; minute B) 101; second C) 1023; minute D) 108; second E) 108; hour Ans: D Level of Difficulty: Easy Section: 10.2.C Learning objective: Passive-Mediated Transport

40. In the body hydrogen ions produced from the reaction of carbonic anhydrase are transported into the lumen of the stomach via an ATP utilizing proton pump. The removal of hydrogen ions drives formation of bicarbonate ions and a concentration gradient is formed. Bicarbonate is transported out at the same time that chloride ions are transferred in. Based on this information, which of the following is FALSE? A) The pump driving the driving the hydrogen ions into the lumen must undergo a conformational change.

B) The pump driving bicarbonate out and chloride in must be an antiport system.

C) The pump driving bicarbonate out and chloride in must require ATP directly.

D) The bicarbonate-chloride pump requires ATP indirectly.

E) The bicarbonate-chloride pump must require activity of the proton pump.

Ans: C Level of Difficulty: Difficult Section: 10.3.C Learning objective: Active Transport

41. Based on the diagram below, which of the following statements is TRUE?

A) F requires ATP directly B) B is an example of symport C) B is gradient driven D) B requires ATP directly E) None of the above are true Ans: E Level of Difficulty: Difficult Section: 10.3.C Learning objective: Active Transport

42. Based on the figure below, this system represents _______.

A) primary active transport B) passive transport C) nonmediated transport D) secondary active transport E) A and D Ans: A Level of Difficulty: Moderate Section: 10.3.C Learning objective: Active Transport

43. Which of the following methods will allow you to determine if a substance used mediated transport?

A) Measure the rate of transport to determine if it is high or low relative to other transport systems.

B) Evaluate the flux at several different concentrations of the substance and look for hyperbolic dependence.

C) Monitor transport rates at a variety of concentrations and confirm a linear dependence.

D) Compare rate of transport in an in vitro system to those in vivo.

E) None of the above.

Ans: B Level of Difficulty: Moderate Section: Box 10-2 Learning objective: Active Transport

44. The greater the magnitude of the concentration gradient: A) the more rapid the rate of diffusion.

B) the more likely mediated transport is required.

C) the easier it is to reverse the flux.

D) the higher number of ATPs required to diffuse.

E) All of the above are true.

Ans: A Level of Difficulty: Moderate Section: 10.1 Learning objective: Thermodynamics of Transport

45. The E. coli maltoporin utilizes what has been termed the greasy slide. Which of the following statements best describe the function of the greasy slide?

A) There is a pathway of phospholipids that line the inside of the channel and facilitate transport.

B) A series of aromatic side chains arrange in a helical pattern matching the relative curvature of the protein backbone, thus provided little restriction to transport.

C) Hydroxyl groups on glucose hydrogen bond with polar and charged side chains lining the channel, thus resulting in a series of interactions mimicking a screw-like pathway.

D) Constriction in the channel removes waters of hydration, thus making the substrate more hydrophobic and "greasy."

E) Amino acids side chains lining the channel are small and non-bulky, making steric constriction essentially non-existent.

Ans: C Level of Difficulty: Moderate Section: 10.2B Learning objective: Passive-Mediated Transport 46. Of the transport proteins discussed in the chapter, in general, which of the following do they have in common?

A) utilize conformational changes to control flux B) require hydrophobic amino acid side chains to line the pores C) utilize stereospecifcity to selectively transport D) transport ionized substances E) move in the direction of the gradient Ans: A Level of Difficulty: Moderate Section: 10.2E Learning objective: Passive-Mediated Transport

47. A patient has low levels of potassium. Which of the following could be affected?

I. levels of calcium available for cardiac muscle II. amount of glucose transported through the intestinal lumen III. amount of lactose metabolized IV. chloride ion transport may slow A) I, IV B) II, IV C) II, III D) II, IV E) I, II, IV Ans: E Level of Difficulty: Difficult Section: 10.3.A, B, C, D Learning objective: Active Transport

48. What type of gradient is required for efficient lactose transport in E. coli?

A) sodium B) potassium C) proton D) magnesium E) calcium

Ans: C Level of Difficulty: Easy Section: 10.3.D Learning objective: Active Transport

49. Which of the following correctly describes the reason for the specificity of valinomycin?

A) The K+ ion is the only ion small enough to fit through the ion channel.

B) The K+ radius is the ideal size for a large binding affinity because it minimizes steric strain and potential for degrees of rotation.

C) It selectively binds to the entrance of the transporter which is lined with negatively charged amino acids.

D) All of the above describe the specificity.

E) None of the above describe the specificity.

Ans: B Level of Difficulty: Difficult Section: 10.2.A Learning objective: Passive-Mediated Transport

50. Which of the following is evidence for aquaporins?

A) Kidney cells are otherwise incapable of maintaining a gradient.

B) Kidney cell transport of water molecules can be inhibited by mercuric ions.

C) Water, a polar substance, cannot cross the hydrophobic membrane without mediation.

D) Rapid rates of water transport require mediation.

E) Studies measuring flux of water molecules in the kidney yielded only linear plots of flux vs.

[H2O] despite the large excess in water.

Ans: B Level of Difficulty: Moderate Section: 10.2.C Learning objective: Passive-Mediated Transport