MCAT Biology Question #3: Answer and Rationale

3. If the effects of IAA treatment in nerve cells are the same as those observed in myocytes, which feature of an action potential would be most affected by IAA treatment?

A) Initiation of depolarization

B) Rising phase of depolarization

C) Falling phase to undershoot

D) Return to resting potential

Answer Analysis

The correct answer is D.

Rationale: This question necessitates that you draw on your knowledge of Na+K+ ATPase’s role in recovery of nerve cell resting potential after an action potential. Typically, repolarization of a nerve cell will overshoot the resting potential, making it more negative, a state known as hyperpolarization. Na+K+ ATPase works to restore the initial balance of ions in the cell (the resting potential) after hyperpolarization, by using the hydrolysis of ATP to move Na+ out of the cell, and K+ into the cell, against their concentration gradients. Based on the information within the passage, you are asked to reason about the effect of IAA treatment and how glycolysis inhibition by IAA will affect cellular concentration of ATP. Based on these two lines of reasoning, you can propose a hypothesis about which portion of an action potential would be affected by IAA treatment.

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