Membrane Potential and Electrochemical Gradients (2A) - MCAT Biological and Biochemical Foundations of Living Systems
Card 1 of 24
What is the primary active transporter that maintains $Na^+$ and $K^+$ gradients in animals?
What is the primary active transporter that maintains $Na^+$ and $K^+$ gradients in animals?
Tap to reveal answer
Na$^+$/K$^+$-ATPase. This pump actively maintains steep Na$^+$ and K$^+$ gradients essential for cellular function and excitability.
Na$^+$/K$^+$-ATPase. This pump actively maintains steep Na$^+$ and K$^+$ gradients essential for cellular function and excitability.
← Didn't Know|Knew It →
What is the Na$^+$/K$^+$-ATPase transport stoichiometry per ATP hydrolyzed?
What is the Na$^+$/K$^+$-ATPase transport stoichiometry per ATP hydrolyzed?
Tap to reveal answer
$3\ Na^+$ out and $2\ K^+$ in. The unequal exchange creates concentration gradients crucial for resting potential and secondary transport.
$3\ Na^+$ out and $2\ K^+$ in. The unequal exchange creates concentration gradients crucial for resting potential and secondary transport.
← Didn't Know|Knew It →
What is the major extracellular anion in animal cells?
What is the major extracellular anion in animal cells?
Tap to reveal answer
$Cl^-$. Chloride's abundance extracellularly balances cationic charges and contributes to Donnan equilibrium.
$Cl^-$. Chloride's abundance extracellularly balances cationic charges and contributes to Donnan equilibrium.
← Didn't Know|Knew It →
What is the major extracellular cation in animal cells?
What is the major extracellular cation in animal cells?
Tap to reveal answer
$Na^+$. High extracellular Na$^+$ concentration is essential for osmotic balance and action potential generation.
$Na^+$. High extracellular Na$^+$ concentration is essential for osmotic balance and action potential generation.
← Didn't Know|Knew It →
What is the major intracellular cation in animal cells?
What is the major intracellular cation in animal cells?
Tap to reveal answer
$K^+$. High intracellular K$^+$ concentration is maintained by active transport and supports resting membrane potential.
$K^+$. High intracellular K$^+$ concentration is maintained by active transport and supports resting membrane potential.
← Didn't Know|Knew It →
What does it mean for a membrane to be selectively permeable to $K^+$ at rest?
What does it mean for a membrane to be selectively permeable to $K^+$ at rest?
Tap to reveal answer
$P_{K}$ is high; $V_m$ is driven toward $E_{K}$. High potassium permeability allows K$^+$ fluxes to dominate, pulling the membrane potential toward its equilibrium.
$P_{K}$ is high; $V_m$ is driven toward $E_{K}$. High potassium permeability allows K$^+$ fluxes to dominate, pulling the membrane potential toward its equilibrium.
← Didn't Know|Knew It →
Which direction does an anion move if $V_m - E_X$ is positive?
Which direction does an anion move if $V_m - E_X$ is positive?
Tap to reveal answer
Into the cell (net inward anion flux). A positive driving force attracts negatively charged ions inward across the membrane.
Into the cell (net inward anion flux). A positive driving force attracts negatively charged ions inward across the membrane.
← Didn't Know|Knew It →
Which direction does a cation move if $V_m - E_X$ is positive?
Which direction does a cation move if $V_m - E_X$ is positive?
Tap to reveal answer
Out of the cell (net outward cation flux). A positive driving force repels positively charged ions outward across the membrane.
Out of the cell (net outward cation flux). A positive driving force repels positively charged ions outward across the membrane.
← Didn't Know|Knew It →
What is the electrochemical driving force expression for ion $X$?
What is the electrochemical driving force expression for ion $X$?
Tap to reveal answer
$V_m - E_X$. This difference quantifies the net force driving ion movement away from its equilibrium potential.
$V_m - E_X$. This difference quantifies the net force driving ion movement away from its equilibrium potential.
← Didn't Know|Knew It →
What condition defines electrochemical equilibrium for ion $X$ across a membrane?
What condition defines electrochemical equilibrium for ion $X$ across a membrane?
Tap to reveal answer
$V_m=E_X$ (no net driving force for $X$). At equilibrium, the membrane potential equals the ion's Nernst potential, resulting in zero net electrochemical force.
$V_m=E_X$ (no net driving force for $X$). At equilibrium, the membrane potential equals the ion's Nernst potential, resulting in zero net electrochemical force.
← Didn't Know|Knew It →
What is the definition of membrane potential ($V_m$) in a cell?
What is the definition of membrane potential ($V_m$) in a cell?
Tap to reveal answer
Voltage across the membrane: $V_{in} - V_{out}$. Convention defines membrane potential as the difference between intracellular and extracellular voltages.
Voltage across the membrane: $V_{in} - V_{out}$. Convention defines membrane potential as the difference between intracellular and extracellular voltages.
← Didn't Know|Knew It →
What sign is the resting membrane potential of most neurons (inside relative to outside)?
What sign is the resting membrane potential of most neurons (inside relative to outside)?
Tap to reveal answer
Negative (inside is negative relative to outside). Ion gradients and selective permeability result in a negatively charged interior relative to the exterior at rest.
Negative (inside is negative relative to outside). Ion gradients and selective permeability result in a negatively charged interior relative to the exterior at rest.
← Didn't Know|Knew It →
What is the typical resting membrane potential magnitude for many neurons?
What is the typical resting membrane potential magnitude for many neurons?
Tap to reveal answer
Approximately $-70\ \text{mV}$. This value arises from the balance of ion concentrations and permeabilities, particularly high K$^+$ conductance.
Approximately $-70\ \text{mV}$. This value arises from the balance of ion concentrations and permeabilities, particularly high K$^+$ conductance.
← Didn't Know|Knew It →
What is the formula for the Nernst equilibrium potential for ion $X$?
What is the formula for the Nernst equilibrium potential for ion $X$?
Tap to reveal answer
$E_X=\frac{RT}{zF}\ln\left(\frac{[X]{out}}{[X]{in}}\right)$. The equation balances the chemical concentration gradient with the electrical potential difference at equilibrium.
$E_X=\frac{RT}{zF}\ln\left(\frac{[X]{out}}{[X]{in}}\right)$. The equation balances the chemical concentration gradient with the electrical potential difference at equilibrium.
← Didn't Know|Knew It →
At $37^\circ\text{C}$, what is the common base-$10$ Nernst form for a monovalent ion?
At $37^\circ\text{C}$, what is the common base-$10$ Nernst form for a monovalent ion?
Tap to reveal answer
$E_X\approx\frac{61\ \text{mV}}{z}\log\left(\frac{[out]}{[in]}\right)$. At body temperature, the constant simplifies the natural log form to base-10 for easier physiological calculations.
$E_X\approx\frac{61\ \text{mV}}{z}\log\left(\frac{[out]}{[in]}\right)$. At body temperature, the constant simplifies the natural log form to base-10 for easier physiological calculations.
← Didn't Know|Knew It →
If $V_m$ becomes more permeable to $Na^+$, which direction does $V_m$ shift?
If $V_m$ becomes more permeable to $Na^+$, which direction does $V_m$ shift?
Tap to reveal answer
Toward $E_{Na}$ (depolarizes; becomes more positive). Increased Na$^+$ permeability allows influx, shifting potential toward Na$^+$'s positive equilibrium value.
Toward $E_{Na}$ (depolarizes; becomes more positive). Increased Na$^+$ permeability allows influx, shifting potential toward Na$^+$'s positive equilibrium value.
← Didn't Know|Knew It →
Which ion is closer to electrochemical equilibrium at rest if $V_m$ is near $-70\ \text{mV}$?
Which ion is closer to electrochemical equilibrium at rest if $V_m$ is near $-70\ \text{mV}$?
Tap to reveal answer
$K^+$ (since $V_m$ is near $E_K$). At resting potential, the driving force for K$^+$ is smaller than for other ions due to high K$^+$ permeability.
$K^+$ (since $V_m$ is near $E_K$). At resting potential, the driving force for K$^+$ is smaller than for other ions due to high K$^+$ permeability.
← Didn't Know|Knew It →
Identify the sign of $E_X$ for an anion when $[X]{out} > [X]{in}$.
Identify the sign of $E_X$ for an anion when $[X]{out} > [X]{in}$.
Tap to reveal answer
Negative ($E_X<0$). Higher external concentration favors outward movement, but negative valence results in a negative equilibrium potential.
Negative ($E_X<0$). Higher external concentration favors outward movement, but negative valence results in a negative equilibrium potential.
← Didn't Know|Knew It →
What does the valence term $z$ represent in the Nernst equation?
What does the valence term $z$ represent in the Nernst equation?
Tap to reveal answer
Ion charge (e.g., $+1$, $-1$, $+2$). Valence indicates the ion's charge magnitude and sign, influencing the electrical force in the equilibrium calculation.
Ion charge (e.g., $+1$, $-1$, $+2$). Valence indicates the ion's charge magnitude and sign, influencing the electrical force in the equilibrium calculation.
← Didn't Know|Knew It →
Identify the sign of $E_X$ for a cation when $[X]{out} > [X]{in}$.
Identify the sign of $E_X$ for a cation when $[X]{out} > [X]{in}$.
Tap to reveal answer
Positive ($E_X>0$). Higher external concentration creates an outward chemical gradient, yielding a positive equilibrium potential for cations.
Positive ($E_X>0$). Higher external concentration creates an outward chemical gradient, yielding a positive equilibrium potential for cations.
← Didn't Know|Knew It →
What is the definition of an electrochemical gradient for an ion?
What is the definition of an electrochemical gradient for an ion?
Tap to reveal answer
Combined chemical gradient and electrical gradient. It integrates concentration differences and electrical potential to determine the direction and magnitude of ion flux.
Combined chemical gradient and electrical gradient. It integrates concentration differences and electrical potential to determine the direction and magnitude of ion flux.
← Didn't Know|Knew It →
What change in $V_m$ is called hyperpolarization?
What change in $V_m$ is called hyperpolarization?
Tap to reveal answer
$V_m$ becomes more negative. Increased negativity results from net positive charge efflux or negative charge influx, inhibiting excitability.
$V_m$ becomes more negative. Increased negativity results from net positive charge efflux or negative charge influx, inhibiting excitability.
← Didn't Know|Knew It →
What change in $V_m$ is called depolarization?
What change in $V_m$ is called depolarization?
Tap to reveal answer
$V_m$ becomes less negative (moves toward $0$). Reduction in negativity occurs when net positive charge enters, as in Na$^+$ influx during excitation.
$V_m$ becomes less negative (moves toward $0$). Reduction in negativity occurs when net positive charge enters, as in Na$^+$ influx during excitation.
← Didn't Know|Knew It →
What is the net charge moved per cycle by the Na$^+$/K$^+$-ATPase?
What is the net charge moved per cycle by the Na$^+$/K$^+$-ATPase?
Tap to reveal answer
Net $+1$ out (electrogenic pump). The unequal ion transport generates a net positive charge efflux, contributing to membrane hyperpolarization.
Net $+1$ out (electrogenic pump). The unequal ion transport generates a net positive charge efflux, contributing to membrane hyperpolarization.
← Didn't Know|Knew It →