Deck 4: Ion Channels and Signaling

Question 1

How thick is the plasma membrane of a cell?

A) 0.6 nm
B) 2 nm
C) 6 nm
D) 20 nm
E) 600 nm

Answer 1

C

Question 2

Plasma membrane lipid molecules

A) allow ions to diffuse across the membrane against their concentration gradient.
B) are entirely hydrophobic.
C) allow ions to diffuse across the membrane down their concentration gradient.
D) are arranged with their polar, hydrophilic heads facing outward and their hydrophobic tails extending to the middle of the layer.
E) are arranged with their polar, hydrophilic heads facing inward to the middle of the layer and their hydrophobic tails extending outward.

Answer 2

D

Question 3

The "selectivity filter" in an ion channel is most accurately described as a part of the pore that

A) contains a ring of uncharged residues that interact with specific ions.
B) contains a ring of charged residues that interact with specific ions.
C) contains a ring of charged residues that change conformation to either open or close access through the pore for ions.
D) contains a ring of uncharged residues that change conformation to either open or close access through the pore for ions.
E) interacts with lipids.

Answer 3

B

Question 4

How can protein molecules be positioned in the plasma membrane?

A) Protein molecules are buried in the lipid bilayer of the membrane and are not exposed to either the cytoplasm of the extracellular space.
B) All protein molecules completely span the membrane and face both the cytoplasm and the extracellular space.
C) Protein molecules can face only the extracellular side, only the cytoplasm, or span the membrane completely and face both the extracellular side and the cytoplasm.
D) Protein molecules in the membrane only face the cytoplasm.
E) Protein molecules in the membrane only face the extracellular space.

Question 5

The channel "gate" is best described as a part of the channel

A) pore that contains a ring of uncharged residues that interact with specific ions.
B) pore that contains a ring of charged residues that interact with specific ions.
C) structure that can change shape to either close or open the access through the channel pore.
D) structure that responds directly to changes in voltage across the plasma membrane.
E) pore that aids in stripping water from hydrated ions before they enter the pore.

Question 6

What is a cation?

A) A negatively charged particle
B) An uncharged particle
C) A positively charged particle
D) A negatively charged amino acid residue
E) A positively charged amino acid residue

Question 7

Channel "activation" is a(n)

A) increase in the channel mean open time.
B) decrease in the channel mean open time.
C) increase in the frequency of channel opening.
D) decrease in the frequency of channel opening.
E) increase in the frequency of channel opening and the channel mean open time.

Question 8

What is an anion?

A) A negatively charged particle
B) An uncharged particle
C) A positively charged particle
D) A negatively charged amino acid residue
E) A positively charged amino acid residue

Question 9

Hyperpolarization occurs when the membrane potential

A) does not change.
B) displays rectification.
C) becomes more negative.
D) changes direction.
E) becomes more positive.

Question 10

When a large molecule binds to and physically obstructs the pore of a channel, it is called

A) mechanoreception.
B) ligand gating.
C) an open channel block.
D) channel deactivation.
E) a sensitivity filter.

Question 11

Deactivation occurs when a

A) channel opens in response to a stimulus.
B) ligand-gated ion channels closes in the continued presence of the stimulus to open.
C) voltage-gated ion channel closes in the continued presence of the stimulus to open.
D) channel closes after the stimulus to open has been removed.
E) channel does not respond to a stimulus.

Question 12

Permeability can be defined as

A) the ease with which ions can move across the membrane.
B) the voltage-dependence of activation of an ion channel.
C) the mean open time of a channel.
D) the equilibrium potential of an ion.
E) simple diffusion of ions down their concentration gradient.

Question 13

Channels can be induced to open based on

A) only the voltage across the membrane.
B) only the effects of membrane stretch on the channel.
C) only the effects of ligand binding to the channel.
D) only the effects of either voltage across the membrane, membrane stretch, or ligand binding, but not more than one of these.
E) the effects of voltage across the membrane, membrane stretch, ligand binding, or a mixture of these influences.

Question 14

In the continued presence of the stimulus to open, after opening initially, some voltage-gated channels will close and remain closed for the remainder of the stimulus. This is called

A) activation.
B) inactivation.
C) deactivation.
D) contraction.
E) desensitization.

Question 15

In the continued presence of the stimulus to open, after opening initially, some ligand-gated channels will close and remain closed for the remainder of the stimulus. This is called

A) activation.
B) inactivation.
C) deactivation.
D) contraction.
E) desensitization.

Question 16

What is the diameter of the tip of a microelectrode?

A) 1-3 micrometers
B) 1 millimeter
C) 10 micrometers
D) 100 micrometers
E) less than 0.5 micrometers

Question 17

Microelectrode recording is a method commonly used for accurate measurements of

A) ionic currents through channels.
B) voltage across a cell membrane.
C) the number of channels expressed by a cell.
D) the equilibrium potential of a channel.
E) the mean open time of a channel.

Question 18

If an experimenter wants to apply a neurotransmitter molecule in the middle of a recording session using a patch clamp experiment to measure the effects of the neurotransmitter on ligand-gated ion channels, which experimental approach in most commonly used?

A) Microelectrode recording
B) Intracellular recording
C) Cell-attached patch clamp
D) Outside-out patch clamp
E) Inside-out patch clamp

Question 19

If an experimenter wants to apply a cytoplasmic molecule in the middle of a recording session using a patch clamp experiment to measure the effects of this ligand on ion channels, which experimental approach in most commonly used?

A) Microelectrode recording
B) Whole-cell patch clamp
C) Cell-attached patch clamp
D) Outside-out patch clamp
E) Inside-out patch clamp

Question 20

The "inside-out" patch clamp technique

A) allows the experimenter to easily change the solution bathing the inside surface of the membrane patch during the recording and study the activity of single voltage-gated channel currents.
B) allows the experimenter to easily change the solution bathing the outside surface of the membrane patch during the recording and study the activity of single voltage-gated channel currents.
C) does not allow the experimenter to change the solution on either side of the membrane patch, but you can study the activity of single voltage-gated currents.
D) allows the experimenter to easily change the solution bathing the inside surface of the membrane patch during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).
E) allows the experimenter to easily change the solution bathing the outside surface of the membrane patch during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).

Question 21

The "outside-out" patch clamp technique

A) allows the experimenter to easily change the solution bathing the inside surface of the membrane patch during the recording and study the activity of single voltage-gated channel currents.
B) allows the experimenter to easily change the solution bathing the outside surface of the membrane patch during the recording and study the activity of single voltage-gated channel currents.
C) does not allow the experimenter to change the solution on either side of the membrane patch, but you can study the activity of single voltage-gated currents.
D) allows the experimenter to easily change the solution bathing the inside surface of the membrane patch during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).
E) allows the experimenter to easily change the solution bathing the outside surface of the membrane patch during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).

Question 22

The "whole cell" patch clamp technique

A) allows the experimenter to easily change the solution bathing the inside surface of the cell during the recording and study the activity of single voltage-gated channel currents.
B) allows the experimenter to easily change the solution bathing the outside surface of the cell during the recording and study the activity of single voltage-gated channel currents.
C) does not allow the experimenter to change the solution on either side of the cell, but you can study the summed activity of all voltage-gated channels in the cell (macroscopic current).
D) allows the experimenter to easily change the solution bathing the inside surface of the cell during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).
E) allows the experimenter to easily change the solution bathing the outside surface of the cell during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).

Question 23

The "cell-attached" patch clamp technique

A) allows the experimenter to easily change the solution bathing the inside surface of the membrane patch during the recording and study the activity of single voltage-gated channel currents.
B) allows the experimenter to easily change the solution bathing the outside surface of the membrane patch during the recording and study the activity of single voltage-gated channel currents.
C) does not allow the experimenter to change the solution on either side of the membrane patch, but you can study the activity of single voltage-gated currents.
D) allows the experimenter to easily change the solution bathing the inside surface of the membrane patch during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).
E) allows the experimenter to easily change the solution bathing the outside surface of the membrane patch during the recording and study the summed activity of all voltage-gated channels in the cell (macroscopic current).

Question 24

What is the diameter of the tip of a pipette used for patch clamp recording?

A) Less than 0.5 micrometers
B) 1 micrometer
C) 1 millimeter
D) 100 micrometers
E) 10 millimeters

Question 25

The conductance of a channel depends on which two factors?

A) The voltage across the plasma membrane and the concentration of ions
B) Channel permeability and the voltage across the plasma membrane
C) The mean open time of the channel and the concentration of ions
D) Channel permeability and the concentration of the ions
E) The mean open time of the channel and the channel permeability

Question 26

Conductance characteristics of a channel can be specified precisely by determining

A) a slope conductance.
B) a chord conductance.
C) a complete current-voltage relation and by specifying the ionic conditions under which it was obtained.
D) an averaging of the slope conductance and the chord conductance.
E) the driving force.

Question 27

Driving force on a specific ion is

A) the voltage-dependence of activation for that ion channel.
B) equal to the voltage across the membrane minus the equilibrium potential for the ion.
C) equal to the equilibrium potential for the ion.
D) equal to the concentration gradient across the membrane for the ion.
E) equal to the conductance through channels for the ion.

Question 28

Under which of the following conditions would the current-voltage relation for a channel be nonlinear?

A) When the voltage across the plasma membrane is very negative
B) When the ion concentrations on either side of the channel are symmetrical, or because the channel itself is nonrectifying
C) When the ion concentrations on either side of the channel are not symmetrical, or because the channel itself is rectifying
D) When the equilibrium potential for the channel is at zero millivolts
E) When the mean open time of the channel randomly varies

Question 29

If the potassium ion concentration is 3 mM outside and 88 mM in the cytoplasm, and potassium selective channels open with the membrane potential at -85 mV, which will occur?

A) The net flux of potassium ions will be inward.
B) The net flux of potassium ions will be outward.
C) There will be no net flux of potassium ions-it will be equal in and out.
D) There will be no movement of potassium ions across the membrane.
E) Potassium channels will inactivate.

Question 30

If the potassium ion concentration is 3 mM outside and 88 mM in the cytoplasm, and potassium selective channels open with the membrane potential at -95 mV, which will occur?

A) The net flux of potassium ions will be inward.
B) The net flux of potassium ions will be outward.
C) There will be no net flux of potassium ions-it will be equal in and out.
D) There will be no movement of potassium ions across the membrane.
E) Potassium channels will inactivate.

Question 31

If the sodium ion concentration is 130 mM outside and 12 mM in the cytoplasm, and sodium selective channels open with the membrane potential at +80 mV, which will occur?

A) The net flux of sodium ions will be inward.
B) The net flux of sodium ions will be outward.
C) There will be no net flux of sodium ions-it will be equal in and out.
D) There will be no movement of sodium ions across the membrane.
E) Sodium channels will inactivate.

Question 32

Increasing the concentration of sodium ions on the outside of the membrane (for example, increasing sodium outside from 130 to 200 mM)

A) does not change the sodium ion equilibrium potential.
B) makes the sodium ion equilibrium potential more negative.
C) makes the sodium ion equilibrium potential more positive.
D) changes the mean open time of sodium channels.
E) changes the electrostatic charges within the pore of the channel.

Question 33

What governs the movement of ions through channels in the plasma membrane?

A) Ions move through such channels passively, driven by concentration gradients and by the electrical potential across the membrane.
B) Ions move through channels actively, driven by the energy provided by ATP.
C) Ions move through channels passively, driven only by the concentration gradient.
D) Ions move through channels passively, driven only by the electrical potential across the membrane.
E) Ions move through channels actively, driven by the energy provided by GTP.

Question 34

The equilibrium potential depends on

A) the open state of the channel.
B) the ion concentrations on either side of the membrane.
C) the mechanism for ion permeation through the channel.
D) whether the channel is inactivated.
E) the number of pathways for current flux.

Question 35

At the equilibrium potential

A) the concentration gradient is zero.
B) there is no movement of ions across the plasma membrane.
C) there is an exact balance between forces of the concentration gradient and the electrical potential gradient.
D) there is a maximum movement of ions across the plasma membrane.
E) the electrical potential gradient is zero.

Question 36

When membrane potential is at the equilibrium potential for an ion, there is/are

A) an inward net movement of ions.
B) no net movement of ions across the membrane (equal in and out).
C) an outward net movement of ions.
D) no movement of ions in either direction (in or out).
E) equal numbers of the permeant ion inside and outside the cell.

Question 37

Increasing the concentration of potassium ions on the outside of the membrane (for example, increasing potassium outside from 3 to 20 mM)

A) does not change the potassium ion equilibrium potential.
B) makes the potassium ion equilibrium potential more negative.
C) makes the potassium ion equilibrium potential more positive.
D) changes the mean open time of potassium channels.
E) change the electrostatic charges within the pore of the channel.

Question 38

If the potassium ion concentration is 3 mM outside and 88 mM in the cytoplasm, and potassium selective channels open with the membrane potential at -30 mV, which will occur?

A) The net flux of potassium ions will be inward.
B) The net flux of potassium ions will be outward.
C) There will be no net flux of potassium ions-it will be equal in and out.
D) There will be no movement of potassium ions across the membrane.
E) Potassium channels will inactivate

Question 39

If the sodium ion concentration is 130 mM outside and 12 mM in the cytoplasm, and sodium selective channels open with the membrane potential at -30 mV, which will occur?

A) The net flux of sodium ions will be inward.
B) The net flux of sodium ions will be outward.
C) There will be no net flux of sodium ions-it will be equal in and out.
D) There will be no movement of sodium ions across the membrane.
E) Sodium channels will inactivate.

Question 40

The equilibrium potential for a channel can be described as proportional to the

A) difference between the concentration inside the cell and outside the cell.
B) between the logarithms of the concentration inside the cell and outside the cell.
C) addition of the logarithms of the concentration inside the cell and outside the cell.
D) addition of the concentration inside the cell and outside the cell.
E) multiplication of the logarithms of the concentration inside the cell and outside the cell.

Question 41

A "rectifiying" channel

A) does not conduct ions because the pore is closed.
B) conducts ions equally in both directions.
C) is better at conducting ions in one direction than the other.
D) inactivates rapidly.
E) deactivates rapidly.

Question 42

Based on the Nernst equation, if the concentration of sodium outside was 130 mM and the concentration of sodium in the cytoplasm was 12 mM, what is the sodium equilibrium potential?

A) -85 mV
B) -30 mV
C) 0 mV
D) +30 mV
E) +60 mV

Question 43

Based on the Nernst equation, if the concentration of potassium outside was 3 mM and the concentration of sodium in the cytoplasm was 88 mM, what is the potassium equilibrium potential?

A) -85 mV
B) -30 mV
C) 0 mV
D) +30 mV
E) +60 mV

Question 44

Eyring rate theory models of ion permeation

A) are based on ion diffusion only.
B) are based on the contribution of electrostatic charges in the pore only on the rate of flux.
C) are based on the contribution of electrostatic charges in the pore only on ion selectivity.
D) incorporate the effects of electrostatic charges in the pore on ion selectivity and the rate of flux.
E) incorporate the effects of electrostatic charges in the pore and the voltage across the membrane.

Question 45

Ion permeation can be described as

A) simple diffusion of ions down their concentration gradient.
B) active transport of ions against their concentration gradient.
C) facilitated transport of ions against their concentration gradient.
D) hopping or jumping of ions along electrostatic binding sites in the pore driven by the concentration gradient and the charge across the membrane.
E) hopping or jumping of ions along electrostatic binding sites in the pore driven by the concentration gradient.

Question 46

Even though channels have a mean open time, what causes the measured openings of the channel to vary randomly around this mean?

Question 47

For two ions that have almost exactly the same radius (sodium and calcium), how can voltage-gated ion channels be selectively permeable to one or the other?

Question 48

How do channels in the plasma membrane cause a depolarization of membrane potential?

Question 49

What does the "gate" on an ion channel do?

Question 50

Compare and contrast voltage-activated channels, mechanocreptor channels, and ligand-activated channels.

Question 51

When you compare the current across a muscle cell membrane before and after applying acetylcholine, you notice that acetylcholine causes to a large inward current and that there is also an increase in the baseline fluctuations (or "noise") in the recorded current. What causes this "noise"?

Question 52

Briefly explain the principle of "noise analysis."

Question 53

Why is a high resistance seal (a "giga-seal") required to perform patch clamp recordings?

Question 54

Why do cell attached recordings of single channel openings look like square steps?

Question 55

When using patch clamp recording, what is the difference between an "inside-out patch" and an outside-out patch"?

Question 56

What is advantage of using a "perforated patch" recording technique instead of a traditional "whole-cell recording" technique?

Question 57

Describe the methods for forming a whole-cell patch clamp recording.

Question 58

The conductance of an ion channel can be measured is several ways. Explain the difference between "chord conductance" and "slope conductance," and indicate when these two calculations might yield different values?

Question 59

Can voltage-gated ion channels ever move an ion against its concentration gradient? If so, when does this occur?

Question 60

Define and explain the equilibrium potential for an ion.

Question 61

Using the Nernst equation, what would you calculate the equilibrium potential for the sodium ion to be if the concentration of sodium outside was 130 mM, and the concentration of sodium in the cytoplasm was 12 mM?