Deck 10: Transmembrane Transport of Ions and Small Molecules

Question 1

How does uniport transport compare with simple diffusion?

A)Similar to simple diffusion,uniport transport is nonspecific.
B)Uniport transport is slower but more specific than simple diffusion.
C)Uniport transport is much faster and more specific than simple diffusion.
D)Simple diffusion is reversible but uniport transport is not.

Answer 1

C

Question 2

Amino acid entry into cells can occur via uniporters or symporters.If the rate of leucine entry into the cell increases when the pH decreases,this suggests:

A)leucine is being transported by a uniporter.
B)leucine is being actively pumped across the membrane against its concentration gradient.
C)leucine is being transported by a H⁺ symporter.
D)leucine is crossing the membrane via simple diffusion.

Answer 2

C

Question 3

The major ATP-powered pump responsible for maintaining ion gradients across the plasma membrane of mammalian cells is:

A)the calmodulin-activated plasma membrane Ca²⁺ ATPase.
B)the sarcoplasmic reticulum Ca²⁺ ATPase.
C)the vacuolar F-class proton pump.
D)the plasma-membrane Na⁺/K⁺ ATPase.

Answer 3

D

Question 4

In a laboratory activity,red-labeled glucose,blue-labeled water,and green-labeled ethanol are added to a solution placed over an artificial,pure phospholipid membrane.Which colors will be observed on the other side of the membrane after 10 minutes?

A)red
B)blue
C)green
D)b and c

Question 5

The osmotic potential of a hypotonic solution should cause an animal cell to _____,but with frog oocytes prevent this effect by _____.

A)burst;not expressing aquaporins
B)shrink;not expressing aquaporins
C)burst;expressing more aquaporins
D)shrink;expressing more aquaporins

Question 6

Classes of membrane transport proteins include all of the following EXCEPT:

A)ATP-powered pumps.
B)ion channels.
C)protein translocons.
D)transporters.

Question 7

In which of the following cases is energy NOT needed for transmembrane transport?

A)Lysine moves into the cell against its concentration gradient via the Na⁺/lysine symporter.
B)Potassium ions (K⁺)move out of the cell down the K⁺ concentration gradient via potassium channels.
C)Glucose moves into the cell down its concentration gradient via a glucose uniporter.
D)The second and third answers are correct.
E)all of the above

Question 8

What is the approach that plants use to respond to differences in osmotic pressure between the inside and outside of the cell?

Question 9

Which of the following is true about glucose transporters?

A)GLUT-2 and GLUT-4 are expressed on all cell types.
B)All the members of the GLUT family have the same affinity for glucose.
C)Cells that express GLUT-1 and GLUT-3 display more glucose uptake than cells expressing GLUT-2 at physiological blood concentrations (5 mM).
D)GLUT proteins are specific for glucose molecules and will not transport other sugars.

Question 10

The partition coefficient K,the equilibrium constant for partitioning between oil and water,for butyric acid is about 10-²,and for 1,4-butanediol it is about 10-⁴.You add liposomes containing only water to a solution with an initial concentration of 1 mM butyric acid and 100 mM 1,4-butanediol outside the liposomes.What is the relative rate of diffusion of the two substances into the liposome interior?

A)Butyric acid diffuses into the liposome 100-fold faster than butanediol.
B)The two diffuse into the liposome at equal rates.
C)Butanediol diffuses into the liposome 100-fold faster than butanediol.
D)Not enough information is provided to permit an answer.

Question 11

Glucose enters erythrocytes via a GLUT-1 uniporter.As the levels of glucose in the bloodstream decrease between meals,what happens to the glucose in the cells?

A)Glucose leaves the cell through the GLUT-1 uniporter,traveling down the new concentration gradient.
B)Glucose remains in the cell because uniporters can only transport in one direction.
C)Glucose remains in the cell because the GLUT-1 uniporters are gated and the gates close at low glucose concentrations.
D)Glucose remains in the cell because it has been phosphorylated and no longer has affinity for the GLUT-1 uniporter.

Question 12

The glucose uniporter GLUT1 has a Km of 1.5 mM for d-glucose and 30 mM for d-galactose.At a concentration of 5 mM for each,what is the rate of glucose transport relative to galactose transport? The Vmₐₓ may be assumed to be the same for both.

A)3.7-fold slower
B)equal
C)5.5-fold faster
D)20-fold faster

Question 13

Which statement describes the mode of action of the ABCB1 transporter (the first eukaryotic ABC transporter to be recognized)?

A)During transport,the ligand binding site is alternately exposed to the exoplasmic and the cytoplasmic side of the membrane.
B)During transport,a conserved aspartate residue is phosphorylated.
C)This class of pumps transports only H⁺ ions.
D)This transporter acts as a chloride channel.

Question 14

Which of the four classes of ATP-powered pumps share overall similarity: several subunits,the same general organization,and a similar function as H⁺ transporters?

A)ABC superfamily and P-class pumps
B)ABC superfamily and P-class pumps
C)F-class pumps and P-class pumps
D)F-class pumps and V-class pumps

Question 15

When computing the osmotic pressure that must be placed across the membrane to stop the flow of water,what is the glucose osmotic equivalent of 1 M CaCl₂?

A)1 M
B)2 M
C)3 M
D)4 M

Question 16

Describe how aquaporins facilitate the movement of water across the plasma membrane.

Question 17

ABC superfamily proteins are thought to act as ATP-dependent flippases in transporting:

A)lipophilic drugs out of mammalian cells.
B)Ca²⁺ out of mammalian cells.
C)H⁺ out of mammalian cells.
D)Na⁺ out of mammalian cells,K⁺ into mammalian cells.

Question 18

Which of the following statement(s)is (are)true of V-class proton pumps?

A)They are ATPases.
B)They are present in membranes of plant vacuoles.
C)They serve to decrease the pH inside a lysosome.
D)all of the above

Question 19

Both ethanol and glycine are small molecules of approximately equal molecular weight.However,the membrane is much more permeable to ethanol than glycine.What accounts for the large difference in membrane permeability between ethanol and glycine?

Question 20

Aquaporins are:

A)β-barrel proteins in the outer membrane of bacteria.
B)ABC proteins.
C)symporters.
D)water channels.

Question 21

What is the expected effect on salt accumulation in the plant vacuole of a mutation in the plant vacuolar ATPase that decreases the H⁺ concentration in the vacuole?

A)increased Na⁺ accumulation
B)decreased Na⁺ accumulation
C)no effect
D)complete seed germination failure

Question 22

Propose a rationale for why the import of sucrose into the plant vacuole is coupled to the export of H⁺ ion into the plant cytosol.

Question 23

Transepithelial glucose transport uses a symporter to transport glucose up a concentration gradient by:

A)coupling glucose transport to proton movement.
B)coupling glucose transport to Na⁺ movement.
C)coupling glucose transport to Ca²⁺ movement.
D)coupling glucose transport to Cl- movement.

Question 24

What is the basic structural organization of an ABC superfamily transport protein?

Question 25

Why are nongated channels important in the generation of a negative electric potential (voltage)of 50-70 mV inside the cell with respect to the outside?

Question 26

The ΔG calculation for the two-Na⁺/one-glucose symporter includes which of the following terms?

A)RT ln [glucoseᵢn]/[glucoseₒᵤt]
B)2RT ln [Na⁺ᵢn]/[Na⁺ₒᵤt]
C)2FE
D)all of the above

Question 27

Which of the following is true about cystic fibrosis?

A)The normal CFTR channel protein is a chloride uniporter,but CF patients have a mutation that makes it require ATP.
B)CFTR mutations result in a mutated protein,which pumps too many chloride ions out of the cell.
C)There are no treatments for patients with CF that are specifically targeted to the CFTR receptor.
D)Patients with the most common mutation make a CFTR protein that is not present in the membrane.

Question 28

Explain why ATP-powered proton pumps cannot by themselves acidify the lumen of the lysosome.

Question 29

The resting membrane potential in animal cells depends largely on nongated _____ channels.

A)Ca²⁺
B)H⁺
C)K⁺
D)Na⁺

Question 30

What evidence suggests that all of the P-class ion pumps evolved from a common ancestor even though they now transport different ions?

Question 31

The many pumps present in the membrane have interconnected and important functions.Which of the following functions is NOT correct?

A)A P-class pump is involved in muscle relaxation.
B)A V-class pump is involved in maintaining the low pH of lysosomes.
C)A P-class pump is involved in keeping the cytosolic levels of calcium low.
D)A P-class pump is involved in keeping the cytosolic levels of potassium low.

Question 32

Propose a rationale for why the import of amino acids or sugars into cells is typically coupled to Na⁺ ion import.

Question 33

Calculate the ΔG for the movement of Na⁺ from inside a typical mammalian cell to outside.

Question 34

A mutant channel protein is expressed in an oocyte.Compared to patch clamping experiments in oocytes expressing the normal channel,the length of downward deviations is diminished by half.This indicates:

A)the mutant channel doesn't make a functional channel.
B)the mutant channel doesn't stay open as long.
C)the mutant channel opens more frequently.
D)the mutant channel behaves the same as the wild-type channel.

Question 35

How does inhibition of the Na⁺/K⁺ ATPase increase the force of heart muscle contraction?

A)It increases cytosolic Na⁺ and therefore decreases Ca²⁺ export.
B)It increases cytosolic K⁺ and therefore decreases Ca²⁺ export.
C)It decreases cytosolic Na⁺ and therefore decreases Ca²⁺ export.
D)It decreases cytosolic K⁺ and therefore decreases Ca²⁺ export.

Question 36

Ion channels achieve selectivity in transport through all of the following mechanisms EXCEPT:

A)evolution from distinct and different parent proteins.
B)divergent evolution from a single type of channel protein.
C)low activation energy for selective passage of the dehydrated ion.
D)use of P segments to form an ion selectivity filter.

Question 37

The movement of dietary glucose and sodium from the intestine into the bloodstream relies on which of the following transport mechanisms?

A)sodium glucose symporter
B)transcellular transport
C)sodium/potassium ATPase
D)all of the above

Question 38

Describe in general terms how the muscle Ca²⁺ ATPase pumps Ca²⁺ ions from the cytosol into the sarcoplasmic reticulum (SR).

Question 39

Describe the patch-clamping technique.Why do investigators often use frog oocytes in their patch-clamping investigations?

Question 40

The magnitude of the membrane electrical potential is calculated by:

A)the Nernst equation.
B)the Michaelis-Menten equation.
C)the Faraday equation.
D)the Bose-Einstein equation.

Question 41

Parietal cells acidify the stomach contents while maintaining a neutral cytosolic pH by:

A)exporting "excess" cytosolic OH- as HCO₃-.
B)exchanging HCO₃- for Cl-.
C)preserving electroneutrality by accompanying the movement of each Cl- ion into the stomach lumen by a K⁺.
D)all of the above.

Question 42

Transepithelial transport requires a _____ cell layer.

A)polarized
B)sealed
C)polarized and sealed
D)permeable

Question 43

The H⁺/K⁺ ATPase on the apical surface of parietal cells exports H⁺ and imports K⁺.How is the buildup of excess K⁺ ions in the parietal cell cytosol prevented?

Question 44

How can a uniporter,GLUT2,be sufficient for entry of glucose from intestinal epithelial cells into the bloodstream?