Deck 8: Transport Across Membranes: Overcoming the Permeability Barrier

Question 1

Most cells have a negative plasma membrane potential (Vm)because they have

A)equal concentrations of ions on both sides of the membrane.
B)an excess of negatively charged solute molecules inside the cell.
C)an excess of positively charged solute molecules inside the cell.
D)an excess of negatively charged solute molecules outside the cell.
E)an excess of water molecules inside the cell.

Answer 1

B

Question 2

Because the procedure you are using to modify plants requires their cell membranes to be pulled away from the cell walls by plasmolysis,you place the cells in a(n)

A)acid solution.
B)hypotonic solution.
C)isotonic solution.
D)basic solution.
E)hypertonic solution.

Answer 2

E

Question 3

Bacterial porins transport

A)any hydrophilic molecule regardless of size.
B)hydrophilic molecules smaller than 600 Da.
C)any hydrophobic molecule regardless of size.
D)hydrophobic molecules larger than 600 Da.
E)any molecule regardless of properties or size.

Answer 3

B

Question 4

Consider an erythrocyte with an internal glucose concentration of 0.1 mM and an external glucose concentration of 5 mM.Each of the following is true about GLUT1 transport of glucose across the plasma membrane into the cell except

A)K_eq is always equal to 1.
B)ΔG depends on the concentration gradient.
C)inward movement is exergonic.
D)ΔG° is always equal to 0.
E)the rate of GLUT1 transport is faster than that of simple diffusion.

Question 5

Which of the following glucose transporters has properties that facilitate glucose transport out of human liver cells to maintain blood sugar level homeostasis?

A)GLUT1
B)GLUT2
C)GLUT3
D)GLUT4
E)GLUT5

Question 6

Each of the following is true for the mechanism of the Na⁺/K⁺ ATPase pump except

A)the E2 conformation is open to the outside of the cell and has high affinity for K⁺.
B)the E1 conformation is open to the inside of the cell and has high affinity for Na⁺.
C)Na⁺ triggered phosphorylation of the pump stabilizes the E2 conformation.
D)K⁺ triggered dephosphorylation of the pump stabilizes the E2 conformation.
E)Each E1-E2 cycle pumps 3 Na⁺ ions out and 2 K⁺ ions in.

Question 7

The erythrocyte anion exchange protein "ping-pong" transport mechanism involves

A)binding of Cl⁻ on one side of the membrane.
B)binding of bicarbonate ion on one side of the membrane.
C)unidirectional transport of Cl⁻ only out of the cell.
D)two conformational states of the protein.
E)All are involved in the mechanism.

Question 8

Each of the following molecules move across membranes by simple diffusion except

A)oxygen.
B)fatty acids.
C)water.
D)glucose.
E)carbon dioxide.

Question 9

The energy necessary to drive the bacteriorhodopsin proton pump that creates the proton gradient needed for ATP synthesis is generated by

A)a Na⁺ electrochemical gradient across the membrane.
B)a H⁺ concentration gradient across the membrane.
C)a membrane potential of 100 mV across the membrane.
D)ATP hydrolysis by ATP synthase.
E)retinal absorption of light energy.

Question 10

Consider a nerve cell with an internal Cl^- concentration of 50 mM,a membrane potential of 60 mV and an external Cl^- concentration of 100 mM.Each of the following is true for Cl^- import into the cell except

A)import is down a concentration gradient.
B)import is down an electrochemical concentration gradient.
C)import ΔG is positive.
D)import requires energy input.
E)All are true.

Question 11

Which of the following protein types would you predict is defective in kidney water balance disorders?

A)aquaporin
B)porin
C)class ATPase
D)anion exchange protein
E)GLUT

Question 12

Cystic fibrosis is the result of a malfunction of a cellular ABC transporter that transports

A)Cl^−.
B)amino acids.
C)vitamin B₁₂.
D)glucose.
E)a hydrophobic drug.

Question 13

All of the following are true about a partition coefficient except

A)it is the ratio of solubility in an organic solvent to solubility in water.
B)it can be used to predict the probability that an amino acid is part of a transmembrane region of a protein.
C)it is high for a molecule that readily crosses membranes by simple diffusion.
D)it is the concentration at which the rate of transport is half maximal.
E)it depends on the polarity of the molecule.

Question 14

Each of the following is an example of facilitated diffusion except

A)glucose transport by GLUT1.
B)chloride-bicarbonate exchange.
C)aquaporin transport.
D)ion channel transport.
E)oxygen transport.

Question 15

Which of the following is a characteristic of facilitated diffusion (passive transport)of a molecule across a membrane?

A)Its rate is higher than that of simple diffusion of the molecule.
B)It is highly specific for the molecule being transported.
C)The direction of transport is determined by concentration and/or electrochemical gradients.
D)The rate of transport is saturable.
E)All of the above are true.

Question 16

One way in which ions are specifically transported into the cell is via

A)gated channels.
B)simple diffusion.
C)carrier (permease)proteins.
D)uniport transporters.
E)ABC transporters.

Question 17

Knowing the ion concentrations on both sides of the plasma membrane makes it possible to calculate the membrane potential (Vm),because at equilibrium

A)the Faraday constant is 0.
B)ΔG is 1.
C)ΔG is 0.
D)the Vm is always -60 mV.
E)It is not possible to calculate Vm without also knowing the uncharged solute distribution across the membrane.

Question 18

Phosphorylation of glucose following its transport into a cell

A)targets the glucose for transport back out of the cell.
B)decreases glucose transport into the cell by decreasing its concentration gradient across the plasma membrane.
C)increases glucose transport into the cell by increasing its concentration gradient across the plasma membrane.
D)converts glucose into a form that can more easily be exported from the cell.
E)maintains a higher level of glucose outside the cell.

Question 19

Which of the following types of transport occur across the erythrocyte membrane?

A)O₂ and CO₂ passive diffusion
B)aquaporin water transport
C)Cl⁻ bicarbonate ion antiport
D)glucose uniport
E)All of the above are correct.

Question 20

Water moves across the plasma membrane into or out of a cell by osmosis when

A)there is an equal solute concentration on both sides of the membrane.
B)water diffuses through a semipermeable membrane toward a higher solute concentration.
C)water diffuses through a semipermeable membrane toward a lower solute concentration.
D)a high solute concentration opens an aquaporin channel.
E)ATP hydrolysis drives aquaporin transport.

Question 21

Whereas animal cells drive indirect transport with a Na⁺ gradient,most other organisms use

A)a glucose gradient.
B)light energy.
C)an H⁺ gradient.
D)a Ca²⁺ gradient.
E)osmosis.

Question 22

When Peter Agre and colleagues compared frog oocytes expressing aquaporin with control oocytes lacking aquaporin placed in pure water,they found that

A)the control oocytes lacking aquaporin swelled and burst as water was transported into the cells.
B)the oocytes expressing aquaporin swelled and burst as water was transported into the cells.
C)the oocytes expressing aquaporin collapsed as water was transported out of the cells.
D)the oocytes expressing aquaporin first swelled and then collapsed as water was transported into and then back out of the cells.
E)the oocytes expressing aquaporin first collapsed and then swelled as water was transported out and then back into the cells.

Question 23

In carrier protein function kinetics,K_m is the

A)maximal rate of solute transport.
B)solute concentration at which the transport rate is half maximal.
C)initial rate of transport at any concentration.
D)constant rate of transport regardless of concentration gradient.
E)standard free energy change used to calculate the maximal rate of transport.

Question 24

The primary difference between active transport and facilitated diffusion is that active transport is the only one of the two in which

A)transporter proteins are required.
B)the direction of transport is [S]_high → [S]_low.
C)the direction of transport is [S]_low → [S]_high.
D)the S concentration gradient provides the energy necessary for S transport.
E)the mechanism is not saturable.

Question 25

Ion gradients established across membranes by V-type ATPase pumps range from

A)1-10-fold
B)10-100-fold
C)10-1000-fold
D)1-1000-fold
E)10-10,000-fold

Question 26

Which of the following types of ATPase pumps are sensitive to vanadate (which inhibits phosphorylation of the pump during its activity mechanism)?

A)P type
B)V type
C)F type
D)ABC type
E)All are inhibited by vanadate.

Question 27

Which of the following is true for the mechanism of the 2Na⁺/glucose symporter?

A)Binding of 2 Na⁺ to the symporter open to the outside of the cell allows a glucose molecule outside the cell to bind.
B)Binding of Na⁺ and glucose causes the symporter to open to the inside of the cell.
C)Release of 2 Na⁺ ions to the inside of the cells causes release of the glucose molecule.
D)Binding of 2 Na⁺ to the symporter on the inside of the cell causes the symporter to open to the outside of the cell and release of the Na⁺ ions.
E)All of the above are steps in the mechanism.

Question 28

Which type of P-type ATPase would you expect to find is defective in a novel cell line in which you observe that maintenance of the phospholipid asymmetry in the plasma membrane is impaired?

A)type 1
B)type 2
C)type 3
D)type 4
E)type 5

Question 29

The Na⁺/K⁺ ATPase pump actively moves

A)2 Na⁺ in,3 K⁺ out.
B)2 Na⁺ out,3 K⁺ in.
C)3 Na⁺ in 2 K⁺ out.
D)3 Na⁺ out,2 K⁺ in.
E)1 Na⁺ out,1 K⁺ in.

Question 30

Each of the following is a characteristic of active transport mechanisms except

A)sensitivity to inhibitors such as proton pump inhibitors.
B)nondirectionality for moving a solute in either direction across a membrane depending on the solute concentration gradient.
C)coupling transport of a solute down its concentration with transport of another solute up its concentration gradient via a symport or antiport mechanism..
D)moving solutes away from equilibrium across a membrane.
E)coupling a thermodynamically unfavorable (endergonic)process with a favorable (exergonic)process.

Question 31

The graph below shows the concentrations of B and C inside the cell over time when the cell that has imported B and C in Figure 8.1 above is transferred to a solution containing a much lower concentration of B and C.Based on these data and coupled with the data observed above,substance C is transported via

A)active transport.
B)facilitated transport.
C)passive transport.
D)simple diffusion.
E)A,B,and C.

Question 32

All of the following are active transporters except

A)symporters.
B)P-class pumps.
C)permeases.
D)bacteriorhodopsin.
E)ABC transporters.

Question 33

What specific type of P-type ATPase pumps H⁺ to acidify the stomach and is inhibited by proton pump inhibitor drugs used to treat excess stomach acid?

A)type 1
B)type 2
C)type 3
D)type 4
E)type 5

Question 34

Different ABC transporters can transport

A)ions.
B)sugars.
C)amino acids and peptides.
D)polysaccharides.
E)All of the above are correct.

Question 35

Mutations in bacterial porins typically lead to antibiotic resistance by

A)changing the orientation of the porin α-helical transmembrane segments to constrict the size of the channel.
B)changing the stereoisomer specificity of the porin transport.
C)blocking diffusion of the antibiotic through the porin channel.
D)disrupting the voltage difference across the porin channel.
E)reversing water transport through the channel.

Question 36

Although all P-type ATPases use the energy of ATP hydrolysis to transport solutes they differ in which of the following?

A)structure
B)mechanism
C)localization in cells
D)physiological roles
E)All of the above are correct.

Question 37

Which of the following is an example of indirect active transport?

A)Na⁺/K⁺ ATPase
B)aquaporin water transport
C)CFTR Cl⁻ transport
D)Na⁺/glucose symport
E)glucose permease transport

Question 38

Active transport makes it possible for cells to

A)take up nutrients from the environment against concentrations gradients.
B)transport out secretory products and waste material against concentration gradients.
C)maintain nonequilibrium intracellular concentrations of ions such as Na⁺,K⁺,Ca2⁺,and H⁺.
D)establish an electrical potential across the membrane.
E)All of the above are correct.

Question 39

Binding and hydrolysis of ATP in a "cassette" domain is part of the transport mechanism of which of the following types of transporters?

A)ABC type
B)type
C)P type
D)V type
E)All of the above are correct.

Question 40

ABC-type ATPases that inhibit the effectiveness of antitumor drugs by transporting the drugs out of tumor cells are known as

A)multidrug resistance (MDR)transporters.
B)Na⁺-drug antiporters.
C)the cystic fibrosis transmembrane conductance regulator (CFTR).
D)porins.
E)None of the above; no such transporter has been identified in eukaryotes.

Question 41

Osmosis requires a ________ membrane that is ________ to solute molecules and permeable to water molecules.

Question 42

Transmembrane movement of a substance down a concentration gradient with no involvement of membrane proteins is called ________.

Question 43

Explain why the steroid hormone estradiol (MW 272)readily crosses membranes by simple diffusion but the much smaller H⁺ requires transport proteins.

Question 44

Frog oocytes are a useful experimental system for studying transporters,because frog oocytes possess all of the following characteristics except

A)they are large,easily injected cells.
B)they express all transporters known.
C)they express injected heterologous mRNAs.
D)they are relatively inexpensive and easy to obtain.
E)they can be maintained in little more than pure water.

Question 45

The transport of two molecules across the cell membrane in different directions by one transporter is called ________.

Question 46

Gated ion channels include each of the following except

A)voltage-gated channels.
B)ligand-gated channels.
C)mechanosensitive channels.
D)patch clamp-gated channels.
E)All of the above are types of gated channels.

Question 47

Simultaneous transport of two molecules across the cell membrane in the same direction by one transporter is called ________.

Question 48

The bacterium Brucella abortus imports and uses the unusual sugar erythritol.The concentration of erythritol within the B.abortus cell is 10 mM,but the external erythritol concentration is much lower at 0.20 mM.What is the energy requirement (ΔG _inward in kcal/mol)for the inward transport of erythritol at 37°C under these conditions?

Question 49

When erythrocytes are in the capillaries of the lungs,O₂ diffuses ________ and is bound to ________.

Question 50

Urea is a small molecule that is transported out of most cells by passive diffusion,but some cells,including kidney cells,have urea-facilitated transporters.Given an assay to measure the amount of urea on one side of the cell plasma,design an experiment to distinguish which mechanism an uncharacterized cell you have isolated uses to transport urea.Include graphs,if this aids in your discussion.

Question 51

The type of transport ATPase that is reversibly phosphorylated as part of the transport mechanism is the ________ ATPase.

Question 52

Transmembrane movement of a substance down a concentration gradient by a membrane protein is called ________.

Question 53

Transmembrane movement of a substance up a concentration gradient requires ________ transport.

Question 54

When erythrocytes are in the capillaries of body tissues,CO₂ diffuses ________ and is converted to ________.

Question 55

Uptake of food particles by trapping them within an invagination of the plasma membrane is called ________.

Question 56

Why would some cells,such as erythrocytes,express GLUT1,but other cells,such as liver cells,express GLUT2,which has a different kinetic relationship between v (rate of diffusion)and Δ[S] (solute concentration gradient)?

Question 57

What is the mechanism by which expression of an MDR protein affects treatment of cancer cells with an antitumor drug? How might you potentially counter the effect of such transporters?

Question 58

The outer membranes of bacteria,mitochondria,and chloroplasts contain large nonselective channels made of multipass proteins known as ________ in which the transmembrane segment of the protein is composed of a ________.