Question 1

Which of the following best describes the two main components that contribute to the Gibbs free energy change ($$\Delta G_{transport}) $$for the movement of a charged ion across a membrane?

Accepted Answer

The chemical gradient and the electrical gradient

Question 2

Given the equation for the Gibbs free energy change for ion transport: $$\Delta G_{transport} = RT \ln \left( \frac{[C]_{out}}{[C]_{in}} \right) + zF\Delta \Psi$$, what does the term $$zF\Delta \Psi$$ represent?

Accepted Answer

The energy contribution from the electrical gradient

Question 3

A cell has a membrane potential ($$\Delta \Psi) of$$ $$-60 mV ($$inside negative) and a temperature of $$37^\circC. If$$ $$1$$ mole of $$Na^+ is $$moved from outside (150 mM) to inside (10 mM), what is the sign of $$\Delta G_{transport}$$?

Accepted Answer

Negative, because both the chemical and electrical gradients favor influx

Question 4

Which of the following is the correct formula for calculating the energy required to move a charged ion across a membrane?

Accepted Answer

$$\Delta G_{transport} = RT \ln \left( \frac{[C]_{out}}{[C]_{in}} \right) + zF\Delta \Psi$$

Question 5

If the membrane potential ($$\Delta \Psi) is$$ $$-60 mV ($$inside negative), what is the effect on the movement of $$Ca^{2+}$$ ions into the cell?

Accepted Answer

It favors the influx of $$Ca^{2+}$$ due to the negative interior

Question 6

A scientist wants to calculate the energy required to move $$1$$ mole of $$K^+$$ from inside a cell ($$[K^+]_{in} = 140 mM) to $$outside ($$[K^+]_{out} = 4 mM) at$$ $$37^\circC $$with $$\Delta \Psi = -70 mV ($$inside negative). Which step should be performed first?

Accepted Answer

Determine the charge of the ion ($$z)$$

Question 7

Which of the following best explains why the movement of $$Na^+$$ into a neuron is energetically favorable under typical physiological conditions?

Accepted Answer

Both the chemical and electrical gradients drive $$Na^+$$ into the cell

Question 8

If $$RT = 2.48 kJ/$$mol at $$25^\circC$$, $$F = 96,485 C/$$mol, and $$\Delta \Psi = -0.06 V$$, what is the value of $$zF\Delta \Psi$$ for $$Ca^{2+}$$?

Accepted Answer

$$-11.6 kJ/$$mol

Question 9

A mutation causes the membrane potential of a cell to become more positive inside. How would this affect the $$\Delta G_{transport}$$ for $$K^+$$ influx?

Accepted Answer

$$\Delta G_{transport}$$ would become less negative, making influx less favorable

Question 10

Which of the following scenarios would result in the largest positive $$\Delta G_{transport}$$ for $$Na^+$$ movement?

Accepted Answer

$$[Na^+]_{in} \gg [Na^+]_{out}$$ and $$\Delta \Psi is $$positive inside

Question 11

A patient is given a drug that doubles the cytosolic concentration of $$Ca^{2+}$$ without changing the extracellular concentration or membrane potential. What is the effect on $$\Delta G_{transport}$$ for $$Ca^{2+}$$ influx?

Accepted Answer

$$\Delta G_{transport}$$ becomes less negative, making influx less favorable

Question 12

Which of the following best describes why $$\Delta G_{transport}$$ for $$Cl^- is $$typically positive when moving into a cell with a negative membrane potential?

Accepted Answer

The electrical gradient opposes $$Cl^-$$ influx

Question 13

Calculate the $$\Delta G_{transport}$$ for moving $$1$$ mole of $$Na^+$$ from inside the cell ($$5 mM) to $$outside ($$150 mM) at$$ $$37^\circC $$and $$\Delta \Psi = -60 mV ($$inside negative). Use $$R = 8.314 J/($$mol·K), $$T = 310 K$$, $$F = 96,485 C/$$mol.

Accepted Answer

$$+11.6 kJ/$$mol

Question 14

Which of the following changes would make $$\Delta G_{transport}$$ for $$K^+$$ efflux more negative?

Accepted Answer

Increasing $$[K^+]_{in}$$ relative to $$[K^+]_{out}$$

Question 15

A researcher observes that $$\Delta G_{transport}$$ for $$Na^+$$ influx is zero. What does this indicate about the system?

Accepted Answer

The chemical and electrical gradients are exactly balanced

Thermodynamics of Membrane Diffusion: Charged Ions

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