Deck 9: Membrane Transport

Question 1

What is the membrane potential created by a sodium gradient where [Na⁺]_out = 145 mM and [Na⁺]_in = 12mM at 37 $\degree$ C?

A) 67 mV
B) 7.9 mV
C) -7.9 mV
D) -29 mV
E) -67 mV

Answer 1

-67 mV

Question 2

What is the [Na⁺]_in/[Na⁺]_out ratio created by depolarization in a nerve cell if the final potential is +50 mV at 37 $\degree$ C?

A) 6.4 * 10⁶
B) 6.5
C) 1.5
D) 0.15
E) 1.6 * 10^-7

Answer 2

6.5

Question 3

Inside a nerve cell at rest, [Na⁺] is _____ and [K⁺] _____ relative to the concentrations seen outside the cell.

A) high; high
B) high; low
C) low; high
D) low; low
E) low; equal

Answer 3

low; high

Question 4

Nerve cells contain high levels of _____ which is a derivative of _____.

A) phosphatidylethanolamine; palmitic acid
B) cholesterol; isoprene
C) phosphatidylcholine, phosphatidic acid
D) sphingomyelin; sphingosine
E) ganglioside G_M1; ceramide

Question 5

After depolarization of a nerve cell, what event restores the resting potential?

A) K⁺ efflux
B) K⁺ influx
C) Na⁺ efflux
D) Na⁺ influx
E) Cl^- efflux

Question 6

For a cell with [Na⁺]_out = 150 mM and [Na⁺]_in = 15 mM at 37 $\degree$ C, what is the free energy for movement of sodium ions from outside the cell to inside if the potential across the membrane is -60 mV?

A) 11.7 kJ/mol
B) 0.145 kJ/mol
C) -0.145 kJ/mol
D) -11.7 kJ/mol
E) cannot be calculated from given information

Question 7

All known porins are _____ proteins composed of _____.

A) monomeric; seven transmembrane $\alpha$ -helices
B) dimeric; $\beta$ -barrels
C) dimeric; three transmembrane $\alpha$ -helices
D) trimeric; $\beta$ -barrels
E) trimeric; four transmembrane $\alpha$ -helices

Question 8

Which of the following will cause the opening or closing of a gated ion channel?

A) pH change
B) phosphorylation
C) voltage change
D) ligand binding
E) all of the above

Question 9

Which of the following statements regarding membrane transporters is true?

A) a porin is always open but only transports solutes in one direction
B) an ion channel selective for K⁺ will also allow Na⁺ through since both are small enough to fit through the channel
C) amphotericin is able to assemble inside a membrane in such a manner to form a channel through which K⁺ and Na⁺ flow, thus disrupting the ion gradient
D) K⁺ channels can work in both directions, allowing the neuronal action potential to move in multiple directions
E) none of the above

Question 10

Which amino acid in the aquaporin channel hydrogen bonds with water to prevent the movement of protons?

A) Asn
B) Leu
C) Phe
D) Val
E) Ile

Question 11

Which of the following is true regarding the glucose transporter?

A) in addition to glucose, it will transport any other monosaccharide with six carbons
B) binding of glucose causes a conformational change so that the transporter is never open on both sides of the membrane
C) ATP hydrolysis prevents the transporter from working in reverse
D) it is able to transport glucose into a cell against a concentration gradient
E) none of the above

Question 12

The Na,K-ATPase is a(n) _____ that moves Na⁺ from _____ and K⁺ from _____.

A) antiporter; inside to out; outside to in
B) antiporter; outside to in; inside to out
C) symporter; inside to out; inside to out
D) symporter; outside to in; outside to in
E) none of the above

Question 13

The P-glycoprotein is an example of a(n) _____ which has been linked to drug resistance in the treatment of _____.

A) ABC transporter; bacterial infections
B) ABC transporter; cancer
C) Na,K-ATPase; viral infections
D) Na,K-ATPase; parasitic infections
E) none of the above

Question 14

Transport of glucose from the intestine into the intestinal cells is accomplished by a(n) ________. This is an example of ___________.

A) uniporter; passive transport
B) uniporter; primary active transport
C) symporter; primary active transport
D) symporter; secondary active transport
E) antiporter; secondary active transport

Question 15

Which of the following would be the first to occur following opening of Ca²⁺ channels during acetylcholine-mediated neurotransmission to a muscle cell?

A) binding of SNARE complex to synaptic vesicles and pre-synaptic membrane
B) binding of acetylcholine to muscle cell receptors
C) reuptake of acetylcholine by the nerve cell
D) hydrolysis of acetylcholine by acetylcholinesterase
E) release of acetylcholine by the nerve cell

Question 16

Which type of ion channel is blocked by lidocaine, a local anesthetic?

A) K⁺
B) Na⁺
C) pre-synaptic Ca²⁺
D) post-synaptic Ca²⁺
E) none of the above

Question 17

Serotonin reuptake occurs by a(n) _____.

A) uniporter
B) antiporter using Na⁺
C) antiporter using Ca²⁺
D) symporter using Na⁺
E) symporter using Ca²⁺

Question 18

Which of the following is true regarding SNARE complex formation?

A) prior to membrane association, SNARE proteins are in an unfolded state
B) two proteins of the SNARE complex come from the membrane and one from the synaptic vesicle
C) formation of a four-helix complex is critical for membrane association of the vesicle
D) formation of the SNARE complex is thermodynamically favorable, as is membrane fusion
E) all of the above

Question 19

Which of the following occurs during the fusion of a synaptic vesicle and cell membrane?

A) SNARE complexes dissociate to allow membrane fusion to occur
B) addition of triacylglycerols to the membrane allows the bilayer to bow inward
C) selective removal of acyl chains from membrane phospholipids allows the bilayer to bow outward
D) the composition of the two membranes has no effect upon the rate of fusion
E) none of the above

Question 20

The GLUT proteins have little structural resemblance to other transport proteins despite having a similar mechanism of transport.

Question 21

The GLUT transporters have a 12-stranded $\beta$ -barrel structure that spans the membrane of the cell.

Question 22

The two conformational states of the GLUT proteins are ___ thus glucose ___.

Question 23

At the neuromuscular synapse, acetylcholine is stored in vesicles in the ___ while acetylcholine receptors are found on the ___.

Question 24

Pinocytosis is a specific type of exocytosis where small amounts of intracellular material are sequestered in a vesicle followed by membrane fusion and transport of the material to the outside of the cell.

Question 25

During receptor-mediated endocytosis, the movement of the receptor-ligand complex requires the presence of ___ that functions by mediating ___.

Question 26

Exosomes often contain ___ And ___

Question 27

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 D-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.