Sample Midterm Questions Flashcards
Of the following statements, which one is FALSE?
a. G-proteins are composed of three different subunits.
b. The α subunit of a G-protein is the binding site for GTP.
c. G-proteins usually diffuse through the cytoplasm to their effector targets.
d. G-protein coupled receptors are similar in their structures.
e. G-protein coupled receptors can be differentially distributed over the surface of a neuron
(c. is the correct choice because G-proteins are membrane-bound, and therefore cannot diffuse through the cytoplasm)
Which of the following is NOT a common characteristic of “L-type” calcium channels?
a. Block by nitrendepine.
b. Block by verapamil.
c. Permeability to barium ions.
d. Permeability to cobalt ions
e. Activation by Bay K8644
( d. is the correct choice because cobalt BLOCKS nearly all known Ca2+ channels
Which of the following is NOT a characteristic of “T-type” calcium channels?
a. Strong depolarizations are required for activation
b. Small unitary barium conductance.
c. Rapid inactivation
d. Insensitivity to dihydropyridines.
e. Insensitivity to ω-conotoxin G-VI-A
(a. is the correct answer because most obvious characteristic of the T-type channel is the relatively weak depolarizations needed to activate it,)
Two microelectrodes are placed in a nerve cell, one delivers a square-wave current pulse and the other measures the resulting voltage change. Which of the following statements is TRUE?
a. The voltage response will be of constant amplitude throughout the duration of the current pulse.
b. The amplitude of the voltage response is linearly related to the size of the current pulse for both depolarizing and hyperpolarizing currents.
c. The duration of the voltage change is greater than that of the current pulse.
d. The duration of the voltage pulse depends upon the membrane length constant.
e. The increase in voltage produced by any current pulse will always produce membrane hyperpolarization
c. is the correct answer because the capacitance of the membrane slows down the voltage response to a current pulse, making it outlast the pulse. b. is INCORRECT, because if you depolarize a nerve cell strongly enough, you get an action potential!)
P-type Ca2+ channels can be distinguished from N-type channels on the basis of which of the following criteria?
a. Sensitivity of the P channels to Nimodipine and omega conotoxin GVIA.
b. Sensitivity of the N-channel to Ni2+ over Cd2+.
c. Sensitivity of the P channel to low concentrations of omega-Agatoxin IVA.
d. Sensitivity of the P channel to omega-Conotoxin M-VII-C.
e. More negative voltage of activation for the N channel vs. the P channel.
c is correct, since low concentrations of Aga-IVA don’t affect N-channels at all, while they do affect P-type channels.
Neither N nor P are sensitive to nimodipine, P is insensitive to conotoxin GVIA, both are sensitive to conotoxin MVIIC, only the T-channel is more sensitive to nickel, and the voltage of activation is slightly more negative for the P channel than for the N channel
A square step of current is injected into a small round cell with negligible cytoplasmic resistance. Which of the following is expected, if the specific membrane resistance and specific membrane capacitance of this cell are unchanged, but the surface membrane area of this cell was doubled?
a. the input resistance will be doubled.
b. the cell membrane capacitance will be halved.
c. the tau of the voltage response of this cell will be unchanged.
d. the tau of the voltage response of this cell will be doubled.
e. the tau of the voltage response of this cell will be quadrupled
c. the tau of the voltage response of this cell will be unchanged.
Which of the following Hodgkin-Huxley equations for putative voltage gated ion channels would describe the slowest activating channel?
a. G = G(max)x3y
b. G = G(max)x2y
c. G = G(max)x5y
d. G = G(max)x4y
e. G = G(max)x1y
c. G = G(max)x5y
In an experiment the distribution of sulphate ions is manipulated to be 10 mM intracellular and 1 mM extracellular. If the cell has a background anion conductance that is not voltage-gated and selectively permeable to sulphate ions, what is the reversal potential for this conductance?
a. ~ +60 mV
b. ~ +30 mV
c. ~ 0 mV
d. ~ -30 mV
e. ~ +60 mV
A long giant axon was determined to behave essentially like an infinitely long axon with the classical method (involving a sharp electrode impaled half way along the axon’s long axis to inject current, and another voltage recording electrode impaled a various distances from the site of injection). At a distance of 3 length constants from the injecting electrode what is the steady state voltage response relative to that recorded at the site of injection?
a. (1 – (3/e)) fold
b. (1 – (1/(cube root of e)) fold
c. (1/ (3e )) fold
d. (1/ (cube root of e)) fold
e. (1 / e3) fold
e. (1 / e3) fold
Relative to the response at the site of injection, the response reduces to 1/e fold at a distance of one length constant. At the distance of another length constant the response is further reduced to (1/e)2 fold. Therefore at a distance nth length constant the response is reduced to (1/e) raised to the nth power fold.
A group of 3 cells are connected by gap junctions. A patch type electrode was found to have negligible resistance when it was dipped into the extracellular solution bathing these cells. Then this electrode was manipulated to record in the whole-cell mode from one cell in this group. The injection of -1 pA into this cell hyperpolarized its membrane potential by 1 mV. What is the input resistance of this group of cells, as measured from the cell recorded in whole-cell mode?
a. 1/3 Mohm
b. 1 Mohm
c. 3 Mohm
d. 1 /3 Gohm
e. 1 Gohm
e. 1 Gohm
This question is framed to focus on the input resistance of a circuit (with three cells). There is no need to find out how the three cells are coupled as long as the recording condition is defined. You can substitute the value of 10-3 V and 10-12 A into the equation of V/I = R to calculate the value of R.
At the squid axon, what is the half-width (i.e. the duration when the amplitude of the signal was ≥ half of the peak value) of the gating current?
a. ~10 ms
b. ~1 ms
c. ~ 100 μs
d. ~ 10 μs
e. ~ 1 μs
c. ~ 100 μs
This question is directly from a diagram in the lecture notes. You should have a rough idea of the timescales of various currents covered in the lecture for the Hodgkin and Huxley experiments
- Which of the following is a common mechanism for termination of a burst of action potentials.
A. Activation of voltage gated calcium channels by accumulation of intracellular cAMP.
B. Activation of voltage gated sodium channels by membrane depolarization.
C. Activation of inward rectifier potassium channels by intracellular spermine.
D. Activation of potassium channels by accumulation of intracellular calcium.
E. Activation of M-type channels by changes in membrane lipid composition.
Which statement best describes the composition of a voltage gated potassium channel?
A. Four homologous domains connected together by a variable linker.
B. Assembly of four individual subunits, each with a voltage sensing domain, forming a single ion conducting pore.
C. Assembly of four individual subunits, each with a voltage sensor, leading to four ion conducting pores per channel.
D. Multiple transmembrane domains that selectively transport potassium ions in response to voltage.
E. A voltage-sensing domain that is coupled to calmodulin and a single ion conducting pore.
B. Assembly of four individual subunits, each with a voltage sensing domain, forming a single ion conducting pore.
Which of the following statements about M-type channels is false?
A. They are regulated by voltage and acetylcholine signaling.
B. They conduct potassium ions.
C. Opening of M-type channels promotes repetitive firing of neurons.
D. Membrane hyperpolarization promotes deactivation of M-type channels.
E. Some anti-epileptic drugs target M-type channels.
C. Opening of M-type channels promotes repetitive firing of neurons.
Which statement best describes the function of strong inwardly-rectifying potassium (Kir) channels.
A. Kir channels are active near the resting membrane potential but are blocked by intracellular spermine at depolarized voltages.
B. Kir channels have a voltage sensing domain that causes channel closure at depolarized voltages.
C. Kir channels exhibit prominent inactivation leading to preferential conduction of inward potassium currents.
D. Kir channels have a tetrameric structure that may contain voltage-sensitive subunits.
E. Kir channels provide an alternative pathway for calcium ions to enter cells during long action potentials.
A. Kir channels are active near the resting membrane potential but are blocked by intracellular spermine at depolarized voltages.
