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Biol 309
Question Bank
Membrane Transport
Multiple Choice
1. A membrane transport protein has a "transporter" mechanism if:
A. it forms an open pore through which a molecule can diffuse.
B. an electrochemical gradient is necessary for transport to occur.
C. it only allows transport "down" a concentration gradient.
D. molecules are transported in opposite directions across the membrane.
E. it binds to the molecule and changes shape during transport.
2. In a living neuron, an action potential is triggered when:
A. an electrode raises the potential above the threshold level.
B. potassium ions flow into the dendrite.
C. voltage-gated Ca - channels open in the post-synaptic membrane.
D. voltage-gated K - channels close along the axon.
E. ligand-gated Na - channels open in the post-synaptic membrane.
3. A patch-clamp device is used to:
A. measure the strength of an electrochemical gradient.
B. study the properties of individual neurotransmitters.
C. infuse different kinds of ions into of an axon.
D. study the properties of individual membrane channels.
E. None of the above answers are correct.
4. A “passive” membrane transport protein:
A. will require a direct source of energy for the transport to occur.
B. can only transport a molecule ‘down’ a gradient.
C. is most likely to involve a ‘carrier’ type transport mechanism.
D. can move a molecule ‘up’ a gradient if a membrane potential exists.
5. Suppose you were to treat a normal mammalian cell with a substance that inhibits the Na-K
ATPase. Would be the most immediate effect upon the cell?
A. There would be no change at all.
B. The cell’s osmotic balance were be disrupted, and the cell would begin to swell.
C. The cell membrane potential would immediately drop to zero.
D. The cell would very quickly run out of ATP.
E. The cell could not create an action potential.
6. Voltage-gated Na+ Channels:
A. remain open until the membrane potential reaches the threshold value.
B. first transport NA+ into the cell, and then change the direction of transport.
C. spontaneously become inactivated a few microseconds after they open.
D. close, but remain active when an action potential is achieved.
Biol 309
Question Bank
Membrane Transport
Page 1
7. Which of the following statements best describes the operating principle of a voltage-clamp device?
A. It changes the levels of ions inside the cell and then measures the change in membrane
potential.
B. It measures the types of ions that flow through single membrane channels.
C. It measures the speed at which neurotransmitters are released.
D. It sets a voltage across the membrane and measures the resultant ion flow.
8. For a typical animal cell, the membrane potential is determined by the equilibrium distribution of
K+ ions across the cell membrane. Free movement of K+ across the membrane occurs through:
A. the voltage gated K-channel
C. the Na-K pump
B. the K+ leak channel
D. free diffusion
9. Transport across a membrane is said to be ‘coupled’ when
A. two molecules are transported across the membrane in the same direction.
B. membrane transport is coupled to an energy source, such as ATP hydrolysis.
C. transport of one ion down its gradient provides the energy to transport another molecule
against its gradient.
D. both the concentration gradient and membrane potential determine the rate of transport
across the membrane.
10. Based upon the patch-clamp tracing shown here, which one of the following conclusions can be
correctly stated?
A. There are at least two ion channels present
in the membrane.
B. The direction of ion flow across the membrane
reverses each time the channel opens.
C. The channel must be abnormal because
there is variation in the period it remains open.
D. The channel present must be a ligand-gated ion channel.
11. A membrane transporter is said to be ‘gated’ if it:
A. requires the binding of ATP to open.
B. allows molecules to pass in only one direction.
C. participates in the formation of the membrane potential
D. opens in response to a specific stimulus.
12. The membrane potential across the cell membrane is the result of:
A. the difference in concentration of K+ and Na+ on either side of the membrane.
B. more positively-charged ions outside and more negatively-charged ions inside.
C. opening and closing of voltage-gated channels in the membrane.
D. electrodes that generate different charges on either side of the membrane.
13. The electrical signal of the action potential is first converted to a chemical signal at which step?
A. Influx of Ca2+ triggered by voltage-gated Ca2+ Channels.
B. Binding of Ca2+ to receptors on synaptic vesicles.
C. release of neurotransmitter into synaptic cleft.
D. Binding of neurotransmitter to receptors on post-synaptic membrane.
Biol 309
Question Bank
Membrane Transport
Page 2
True or false
1. The passive movement of any type of molecule across the cell membrane is called "osmosis."
2. In animals, Na+ concentration is higher outside of the cell than inside.
3. Transport of a charged molecule across a membrane is always influenced by its electrochemical
gradient.
4. Active transport is necessary when substances must be moved down a gradient.
5. The principal "fixed ion" inside cells is Cl – .
6. Membrane transport proteins principally transport macromolecules such as proteins and
polysaccharides across the membrane.
7. In animal cells, the Na+–K+ pump in the plasma membrane serves principally to regulate osmotic
pressure in the cell.
8. Transport of any substances across the membrane requires an energy source.
9. In plants, the cell wall is the principally barrier to diffusion of molecules into and out of the cytosol.
10. Relatively small movements of ions across a membrane can create large changes in membrane
potential.
Matching
1. Match membrane transporter symmetry
with the correct diagram to the right.
___ antiport
___ uniport
___ symport
2. Channel
__ Voltage-gated Na channels
__ Ligand-gated Na channels
__ Voltage-gated K channels
__ Voltage-gated Ca++ channels
Property
A. opening converts membrane potential to a chemical signal
B. opening releases neurotransmitters into synaptic cleft.
C. opening triggers an action potential in the post-synaptic membrane
D. opening propagates action potential along axon
E. opening restores the resting potential on an axon
Fill-in, etc
1. The __________________________ is created by a difference in charge across a membrane.
When this is coupled to a difference in an ion’s concentration across the membrane a
_________________________ is created.
Biol 309
Question Bank
Membrane Transport
Page 3
2. A membrane transport protein that displays ________________ symmetry will transport two
different molecules across the membrane in the same direction; whereas, if the symmetry were
__________________, the molecules would move in opposite directions. In either case, if the
transport of one of the molecules against its gradient is ‘powered’ by the movement of the
other molecule down its gradient, this is an example ___________________________.
3. A membrane transport protein that creates an aqueous pore through which a molecules can
freely move is an example of a _________________ type transporter, whereas if binding to
and conformation change in the transport protein is required, it has a __________________
type mechanism.
4. Other than membrane transport proteins, what are 3 other ways by which substances can pass across
a membrane.
1) ________________________ 2) ________________________ 3) _________________________
5. The cystic fibrosis transmembrane-conductance regulator (CFTR), which transports Cl- ions down a
gradient, is mutated in people who suffer from cystic fibrosis. Although opening of the CFTR is
regulated by the binding of ATP, hydrolysis of ATP is not necessary for Cl- transport. For this
transporter identify the:
A. symmetry of transport: ______________________
B. mechanism of transport: ______________________
C. energy requirement: ______________________
D. The CFTR is an example of a ‘gated’ transport protein. True / False -- explain:
Other questions
1. This diagram shows the action of the ‘lactose pump’
of bacterial cells. Identify the:
A) mechanism of transport: ___________________
B) symmetry of transport: ___________________
C) energy requirements: ______________
D) All transport processes require as energy source. Briefly describe the energy source for lactose
transport in this example.
Biol 309
Question Bank
Membrane Transport
Page 4
2. This diagram shows the formation of an action potential upon sensing an initial depolarizing
stimulus.
Na channels:
K channels:
A. Identify the states of the Na+ and K+ voltage-gated channels (opened, closed, inactivated)
at each of the points marked along the recording.
B. Draw another line on the figure to show what would have happened to the membrane
potential if there had been no voltage-gated ions channels.
3. Inhibitory neurotransmitters such as GABA trigger the opening of Cl- channels in the post synaptic
membrane. Explain why this will suppress the formation of a new action potential in that membrane
even when excitatory neurotransmitters may also be released at other synapses.
4. Complete this diagram of a synapse, adding and labeling the components needed to transduce an
action potential from the axon terminus to across the synapse to yield another action potential in the
adjoining dendrite. Label all membranes and the components.
Biol 309
Question Bank
Membrane Transport
Page 5
5. Add the membrane transporters and other
components/metabolites to this diagram needed to show
glucose is transported from the intestinal lumen through
endothelial cells to the circulatory system. Explain the
of active and passive transport steps in the transport
process.
how
roles
6. Ca2+ signaling is essential to muscle contraction. An action potential reaching muscle cells causes a
release of Ca2+ into the cytosol from a specialized form of ER called the sarcoplasmic reticulum,
which triggers contraction. Muscle relaxation requires that the Ca2+ be pumped from the cytosol back
into the sarcoplasmic reticulum. Muscle cells possess two Ca2+ transporters essentially to the
contraction and relaxation processes.
1) The “Ca-release channel”, a voltage-gated Ca2+ channel in the sarcoplasmic reticulum that opens
in response to an action potential.
2) A Ca2+ pump, called SERCA, (the Sarco(Endo)plasmic Reticulum Calcium ATPase) that
removes Ca2+ from the cytosol.
A. Diagram a muscle cell showing these two transporters with notations, cellular locations and
orientations. Also diagram the flow of Ca2+ from and to the cell exterior.
Malignant hyperthermia, caused by a mutation inherited as a dominant trait, has symptoms that
include elevated body temperature (hyperthermia) and uncontrolled skeletal muscle contracture
causing muscle rigidity. Brody Disease (a recessive trait) causes muscle cramping during exercise
due to delayed muscle contraction.
B. A mutation to which transporter would cause
Malignant hyperthermia? Explain.
Brody Disease? Explain
Biol 309
Question Bank
Membrane Transport
Page 6