Really Hard MCAT Bio Question. See if you can solve it.

[SonhosDaVida]

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Ok, so it may not be that hard, but I'm having a hard time understanding it. http://offers.aamc.org/hs-fs/hub/259636/file-2239561794-pdf/MCAT_MiniTest_ebook.pdf The 3rd Bio question asks what portion of the Action Potential would be most affected by IAA treatment. Why is it the return to resting potential instead of the falling to undershoot? I thought at undershoot, the action potential would have a hard time turning to the undershoot since there's so much sodium versus potassium in the cell due to IAA treatment. The cell will remain positive and not experience that influx of potassium? The answer is "return to resting potential."

 

[EverStriving]

Return to resting potential is the answer because that is the only stage involving active transport, and therefore the only stage that could be affected by inhibition of energy production.

A. Initiation of depolarization: Unlikely to be affected. This is more determined by what signals the neuron is receiving from other neurons. It is a passive process, just requiring the potential to be depolarized past threshold.

B. Rising Phase: Would be completely unaffected, as this is a completely passive process caused by opening of Na+ voltage-gated channels.

C. Falling Phase: Would be completely unaffected, as this is a completely passive process caused by opening of K+ voltage-gated channels once there has been sufficient depolarization in the rising phase.

D. Return to Resting Potential: This requires active transport to push ions against their concentration and electrochemical gradients. Therefore it requires energy, and would be affected by inhibition of energy production.

 

[SonhosDaVida]

Return to resting potential is the answer because that is the only stage involving active transport, and therefore the only stage that could be affected by inhibition of energy production.

A. Initiation of depolarization: Unlikely to be affected. This is more determined by what signals the neuron is receiving from other neurons. It is a passive process, just requiring the potential to be depolarized past threshold.

B. Rising Phase: Would be completely unaffected, as this is a completely passive process caused by opening of Na+ voltage-gated channels.

C. Falling Phase: Would be completely unaffected, as this is a completely passive process caused by opening of K+ voltage-gated channels once there has been sufficient depolarization in the rising phase.

D. Return to Resting Potential: This requires active transport to push ions against their concentration and electrochemical gradients. Therefore it requires energy, and would be affected by inhibition of energy production.

thank you! but how does IAA inhibit energy production?

 

[EverStriving]

thank you! but how does IAA inhibit energy production?

Third paragraph:

"...the glycolytic inhibitor iodoacetate (IAA). IAA directly prevents the formation of 1,3-bisphosphoglycerate [an intermediate of glycolysis]."

The passage indicates that glycolysis is the source of energy for the Na/K pump, as inhibition of oxidative phosphorylation does not affect ion concentrations (last paragraph after the graph).