Berkeley Review Bio II, section VIII, Q9

[tfontaine2190]

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Addition of DCCD to cells inhibits H+ transport through the mitochondrial F_0 protein. Addition of 2,4-DNP would be expected to:

A. decrease electron transport and decrease ATP synthesis
B. increase electron transport and increase ATP synthesis
C. increase ET and decrease ATP synthesis
D. decrease ET and increase ATP synthesis

My Logic. When the F_0 (atp synthase) is plugged up, the following happens. (1) H+ builds up outside. (2) Builds up to a point where there isn't any H left in the matrix (3) krebs cycle shut down completely (4) NO ATP IS PRODUCE BY SUBSTRATE LEVEL PHOSPHORYLATION (VIA KREBS) OR BY THE ATP SYNTHENASE.

When you put a hole in the membrane. H+ can now flow back into the matrix. Krebs cycle comes back to life. Electron transport chain comes back to life. BUT, since ATP synthase is still plugged up, no ATP is made there. HOWEVER, substrate level phosphorylation via the KREBS CYCLE CAN OCCUR.

SO THE ANSWER SHOULD BE B. more atp is made and ET use increases.

why is that wrong? (correct answer they offer is C.)

 

[jHustle]

Was this question part of a passage? Because if it was a discrete, then LOL. No wonder few people recommend that.

Sorry, can't help 🙂

 

[Jamil]

Addition of DCCD to cells inhibits H+ transport through the mitochondrial F_0 protein. Addition of 2,4-DNP would be expected to:

A. decrease electron transport and decrease ATP synthesis
B. increase electron transport and increase ATP synthesis
C. increase ET and decrease ATP synthesis
D. decrease ET and increase ATP synthesis

My Logic. When the F_0 (atp synthase) is plugged up, the following happens. (1) H+ builds up outside. (2) Builds up to a point where there isn't any H left in the matrix (3) krebs cycle shut down completely (4) NO ATP IS PRODUCE BY SUBSTRATE LEVEL PHOSPHORYLATION (VIA KREBS) OR BY THE ATP SYNTHENASE.

When you put a hole in the membrane. H+ can now flow back into the matrix. Krebs cycle comes back to life. Electron transport chain comes back to life. BUT, since ATP synthase is still plugged up, no ATP is made there. HOWEVER, substrate level phosphorylation via the KREBS CYCLE CAN OCCUR.

SO THE ANSWER SHOULD BE B. more atp is made and ET use increases.

why is that wrong? (correct answer they offer is C.)

I believe you pose a good point, however I also believe you may be over complicating this question more than is necessary. The amount of ATP produced will decrease, relative to what would have been produced if DCCD were not present. This reason this is the case is that although we have now uncoupled the electron transport chain and ATP synthase we are no longer producing any ATP due to the pumping of protons to the mitochondrial matrix. Electron transport will continue as usual due to the presence of 2,4-DNP, however the protons being pumped will remain in the matrix. From the perspective of just the ECT and ATP synthase no ATP is created, thus supporting the claim that ATP synthesis decreases. From the perspective of the entire cell, the perspective which you took, ATP synthesis will decrease if compared to what would have been made if these chemical agents were not present, again also supporting the answer choice.

In the end you are right, the other systems of the body will attempt to compensate, however total ATP production will decrease. Sorry if I rambled more than was necessary.