Q: Which equation would you use to calculate the free energy change ($$\Delta G) $$for the inward transport of an uncharged solute?

$$\Delta G_{\text{inward}} = +RT \ln \frac{[S]_{\text{inside}}}{[S]_{\text{outside}}}$$

Question 1

Which of the following best describes the difference between direct and indirect active transport across a membrane?

Accepted Answer

Direct active transport uses ATP hydrolysis to move solutes directly against their gradient, while indirect active transport couples the movement of one solute down its gradient to drive the movement of another solute up its gradient.

Question 2

Which equation would you use to calculate the free energy change ($$\Delta G) $$for the inward transport of an uncharged solute?

Accepted Answer

$$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}}$$

Question 3

A mammalian neuron has a [K+] inside/[K+] outside ratio of about 30:1 and a [Na+] inside/[Na+] outside ratio of about 0.08:1. What is the main physiological significance of this arrangement?

Accepted Answer

It establishes the electrochemical gradients necessary for nerve impulse transmission and coupled transport.

Question 4

Which of the following is true regarding the E2 conformation of the Na+/K+ ATPase?

Accepted Answer

It binds K+ strongly and Na+ weakly.

Question 5

Which type of ATPase is responsible for pumping protons into organelles such as lysosomes and the Golgi complex?

Accepted Answer

V-type ATPase

Question 6

If the membrane potential ($$V_m) is $$negative, how does this affect the $$\Delta G$$ for the inward transport of Ca$$^{2+}$$ ions?

Accepted Answer

It makes $$\Delta G$$ more negative, favoring inward transport.

Question 7

Which of the following best explains why the Na+/K+ ATPase is considered an allosteric protein?

Accepted Answer

It alternates between two conformational states (E1 and E2) with different ion affinities.

Question 8

A cell uses a Na+/glucose symporter to import glucose against its concentration gradient. What is the immediate energy source for this process?

Accepted Answer

The inward movement of Na+ down its electrochemical gradient.

Question 9

Given the equation $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}}$$, what is the sign of $$\Delta G if$$ $$[S]_{	ext{inside}} \u003c [S]_{	ext{outside}}$$?

Accepted Answer

$$\Delta G is $$negative, and transport is exergonic.

Question 10

Which of the following best describes the role of the Na+/K+ ATPase in animal cells?

Accepted Answer

It maintains the asymmetric distribution of Na+ and K+ across the plasma membrane by using ATP hydrolysis.

Question 11

A bacterium must keep its internal lactose concentration at 10 mM, while the external concentration is 0.2 mM. Using the equation $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}}$$, is energy required for inward transport?

Accepted Answer

Yes, because $$\Delta G is $$positive and transport is against the concentration gradient.

Question 12

Which of the following is a correct formula for calculating the free energy change for the inward transport of a charged solute?

Accepted Answer

$$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}} + zF V_m$$

Question 13

In the context of indirect active transport, why does the rate of amino acid and sugar uptake increase with increasing extracellular Na+ concentration, as shown in the graph?

Accepted Answer

Because the Na+ gradient provides the energy for symport of amino acids and sugars into the cell.

Question 14

A nerve cell has [Cl–] inside = 50 mM, [Cl–] outside = 100 mM, and $$V_m = -60 mV. $$Using the equation $$\Delta G_{	ext{inward}} = +RT \ln \frac{[S]_{	ext{inside}}}{[S]_{	ext{outside}}} + zF V_m$$, what is the effect of the membrane potential on Cl– import?

Accepted Answer

It opposes Cl– import, making $$\Delta G$$ more positive.

Question 15

Which of the following is NOT a type of transport ATPase?

Accepted Answer

G-type ATPase

Question 16

Which of the following best explains why the Na+/K+ pump moves three Na+ ions out for every two K+ ions in?

Accepted Answer

To help maintain the negative membrane potential and the electrochemical gradients of both ions.

Active Transport and Energetics of Membrane Transport in Cells

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