A question on nerves

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anegligibleperson
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A question on nerves

Post by anegligibleperson » Wed Feb 18, 2009 3:14 pm

This question came out in the 2004 biology A-level exams:
Dinitrophenol is a metabolic poison that prevents the production of ATP. What will happen when a resting axon is treated with such a poison?
A) the charge inside the axon membrane becomes more negative
B) the charge outside the axon membrane becomes less positive
C) the charge inside the axon membrane becomes less positive
D) the charge outside the axon membrane does not change

The answer in my answer key says its C, but I can't figure out why. Na-K pumps are not working due to lack of ATP, which leads to K+ ions diffusing out of neuron while a much smaller amount of Na+ diffuses into the neuron... shouldn't the answer be A? please help! Thanks in advance :)

daveinhampton
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Post by daveinhampton » Wed Feb 18, 2009 11:59 pm

The way I see it, and by no means is this 100% definitive, but since phosphate molecules have a negative charge associated with them, the inhibition of the porduction of ATP would allow for more free-roaming negatively-charged phosphates to accumulate, dropping the charge within the axon (ie. less positive).

Hope that helps...

plasmodesmata11
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Post by plasmodesmata11 » Thu Feb 19, 2009 2:42 am

All right... as I see it, the whole Na-K pump idea would hold true, but it's the phrasing of the answer that was confusing.... The inside is not negatively charged; it's just that in comparison the outside is more positive than the inside (creating the voltage gradient). So it doesn't become more negative, but it is less positive.

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