oxidative phosphorylation Q

[Deepa100]

In 1961, British biochemist Peter Mitchell proposed the chemiosmotic theory. Mitchell illustrated how the transfer of electrons in the electron transport chain resulted in the movement of hydrogen ions across the inner mitochondrial membrane. This ion transfer leads to the generation of a pH gradient and an electric potential across the inner mitochondrial membrane. The electrochemical H+ gradient drives the synthesis of ATP by coupling the energetically favorable re-entry of protons into the matrix and the ATP synthesis machinery. This process of ATP synthesis is known as oxidative phosphorylation




Which of the following, if true, would not support the chemiosmotic model?
A)Decoupling agents such as DNP block ATP synthesis.
B)The Krebs cycle's main function is to break down large molecules in order to reduce the electron carriers NAD+ and FAD+.
C)ATP synthesis is blocked when the physical continuity of the mitochondrial membrane is interrupted.
D)Synthesis of ATP is increased when the pH of the intermembrane space is lowered relative to the pH of the mitochondrial matrix.

[Show/hide explanation]

Ans:B

This question is asking you which three choices DO support the model. The fact that the Krebs cycle does indeed break down larger molecules to reduce NAD+ and FAD does not, in itself, lend support to the chemiosmotic model. Choices A, C and D are wrong because all three would support the chemiosmotic model by illustrating that an electrochemical gradient is necessary for ATP synthesis. Decoupling agents do not permit ion exchange across ATP-synthase membrane pumps; the physical continuity of the membrane is necessary for the constant flow of hydrogen ions and for the interaction of proteins involved in the ETC; and, ATP synthesis depends upon a hydrogen ion gradient across the inner mitochondrial membrane. These are the reasons why choices A, C, and D support the chemiosmotic model, which invokes all of these ideas to account for mitochondrial ATP synthesis.

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My Q: Ok, Kerb's cycle does produce NADH and FADH2 but how can that not support the oxidative phosphorylation? Does any one follow the logic of the solution?

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[mosquitoman]

the chemiosmotic model deals with the electron transport chain.. although B is true.. it says nothing about the ETC

 

[Deepa100]

the chemiosmotic model deals with the electron transport chain.. although B is true.. it says nothing about the ETC

Right...

 

[andafoo]

Right...

Lol, funny answer!

 

[andafoo]

In 1961, British biochemist Peter Mitchell proposed the chemiosmotic theory. Mitchell illustrated how the transfer of electrons in the electron transport chain resulted in the movement of hydrogen ions across the inner mitochondrial membrane. This ion transfer leads to the generation of a pH gradient and an electric potential across the inner mitochondrial membrane. The electrochemical H+ gradient drives the synthesis of ATP by coupling the energetically favorable re-entry of protons into the matrix and the ATP synthesis machinery. This process of ATP synthesis is known as oxidative phosphorylation




Which of the following, if true, would not support the chemiosmotic model?
A)Decoupling agents such as DNP block ATP synthesis.
B)The Krebs cycle's main function is to break down large molecules in order to reduce the electron carriers NAD+ and FAD+.
C)ATP synthesis is blocked when the physical continuity of the mitochondrial membrane is interrupted.
D)Synthesis of ATP is increased when the pH of the intermembrane space is lowered relative to the pH of the mitochondrial matrix.

[Show/hide explanation]

Ans:B

This question is asking you which three choices DO support the model. The fact that the Krebs cycle does indeed break down larger molecules to reduce NAD+ and FAD does not, in itself, lend support to the chemiosmotic model. Choices A, C and D are wrong because all three would support the chemiosmotic model by illustrating that an electrochemical gradient is necessary for ATP synthesis. Decoupling agents do not permit ion exchange across ATP-synthase membrane pumps; the physical continuity of the membrane is necessary for the constant flow of hydrogen ions and for the interaction of proteins involved in the ETC; and, ATP synthesis depends upon a hydrogen ion gradient across the inner mitochondrial membrane. These are the reasons why choices A, C, and D support the chemiosmotic model, which invokes all of these ideas to account for mitochondrial ATP synthesis.

==========
My Q: Ok, Kerb's cycle does produce NADH and FADH2 but how can that not support the oxidative phosphorylation? Does any one follow the logic of the solution?

From the looks of it, either they worded their question wrong or put the wrong answer choices. I really don't like these kinds of questions.

 

[CrimsonMirage]

I think this is one of those questions where I just use process of elimination...all the other choices undoubtedly support the model, so...B it is.

(Agreeing with the others though, poorly worded question.)

 

[TheBoondocks]

In 1961, British biochemist Peter Mitchell proposed the chemiosmotic theory. Mitchell illustrated how the transfer of electrons in the electron transport chain resulted in the movement of hydrogen ions across the inner mitochondrial membrane. This ion transfer leads to the generation of a pH gradient and an electric potential across the inner mitochondrial membrane. The electrochemical H+ gradient drives the synthesis of ATP by coupling the energetically favorable re-entry of protons into the matrix and the ATP synthesis machinery. This process of ATP synthesis is known as oxidative phosphorylation




Which of the following, if true, would not support the chemiosmotic model?
A)Decoupling agents such as DNP block ATP synthesis.
B)The Krebs cycle's main function is to break down large molecules in order to reduce the electron carriers NAD+ and FAD+.
C)ATP synthesis is blocked when the physical continuity of the mitochondrial membrane is interrupted.
D)Synthesis of ATP is increased when the pH of the intermembrane space is lowered relative to the pH of the mitochondrial matrix.

[Show/hide explanation]

Ans:B

This question is asking you which three choices DO support the model. The fact that the Krebs cycle does indeed break down larger molecules to reduce NAD+ and FAD does not, in itself, lend support to the chemiosmotic model. Choices A, C and D are wrong because all three would support the chemiosmotic model by illustrating that an electrochemical gradient is necessary for ATP synthesis. Decoupling agents do not permit ion exchange across ATP-synthase membrane pumps; the physical continuity of the membrane is necessary for the constant flow of hydrogen ions and for the interaction of proteins involved in the ETC; and, ATP synthesis depends upon a hydrogen ion gradient across the inner mitochondrial membrane. These are the reasons why choices A, C, and D support the chemiosmotic model, which invokes all of these ideas to account for mitochondrial ATP synthesis.

==========
My Q: Ok, Kerb's cycle does produce NADH and FADH2 but how can that not support the oxidative phosphorylation? Does any one follow the logic of the solution?

Ok, this is an excellent question. When you approach problems such as these, look for the oddman out. Answer choices A, C, and D are directly related to the chemiosmosis hypothesis. If you lower the H+ in the intermembrane space, this means you're moving H+ into it and this energy gradient is used to make ATP. Greater gradient, more energy for each proton to power ATP production. If you decouple the the H+ reentry into matrix to AtP synthase what occurs? Thermogenesis, the H+ is used for heat. Thus if this occured, ATP wouldn't be produced, supports it. Finally, ATP synthase must be on the inner membrane and contain the reentry of H+ ions. The key with all these answer choices, is that they deal directly with chemiosmosis. What does the krebs cycle do, it provides the high energy electrons to POWER chemiosmosis, but doesn't prove it's validity. A big thing for the mcat is to determine which answer choice is different from the others. The krebs cycle was known to produce high energy products, HOWEVER, how the ATP was actually made remained a mystery. Mitchell received the nobel prize in 1978. Basically, if you've seen THE WATERBOY, remember the line, "Where's the bi**h." In this case it's B.

 

[TheBoondocks]

Ok, this is an excellent question. When you approach problems such as these, look for the oddman out. Answer choices A, C, and D are directly related to the chemiosmosis hypothesis. If you lower the H+ in the intermembrane space, this means you're moving H+ into the matrix and this energy fall is used to make ATP. If you decouple the the H+ reentry into matrix to AtP synthase what occurs? Thermogenesis, the H+ is used for heat. Thus if this occured, ATP wouldn't be produced, supports it. Finally, ATP synthase must be on the inner membrane and contain the reentry of H+ ions. The key with all these answer choices, is that they deal directly with chemiosmosis. What does the krebs cycle do, it provides the high energy electrons to POWER chemiosmosis, but doesn't prove it's validity. A big thing for the mcat is to determine which answer choice is different from the others. The krebs cycle was known to produce high energy products, HOWEVER, how the ATP was actually made remained a mystery. Mitchell received the nobel prize in 1978. Basically, if you've seen THE WATERBOY, remember the line, "Where's the bi**h." In this case it's B.

Where did you get this problem?

 

[Deepa100]

Where did you get this problem?

From a kaplan test. Thanks for your explanation, I understand their solution better now.

 

[Vihsadas]

Yeah boondocks is right on the money.

You gotta be on the lookout for questions like this. They ask you "which does not support the chemiosmotic theory", not "which contradicts the chemiosmotic theory".

Remember that those two are very different!

In this problem, even though B does not go against the chemiosmotic theory, it does not offer any supporting evidence for it. Thus, it still fulfills the conditions given the question.

Tricky, but correct.