Oxidative Phosphorylation!

[andafoo]

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Which of the following biological processes will be most affected by the presence of the mutant gene for sickle cell anemia in an individual?

A. Fermentation of pyruvate to lactate and ATP
B. Production of pyruvate and ATP in glycolysis
C. The production of carbon dioxide, water and ATP during the Kreb's cycle and oxidative phosphorylation
D. The production of carbon dioxide and ATP from ADP in the electron transport chain


Explanation
Corrent Answer: C

Sickle cell anemia lowers the oxygen-carrying capacity of red blood cells. This means that less oxygen is reaching the cells for use in cellular respiration. Fermentation of pyruvate to lactate and ATP will occur in the absence of oxygen, which is not the case here. Glycolysis occurs whether oxygen is present or not, so this process will also be unaffected. Option D. states that carbon dioxide is produced through the processes of the Electron Transport Chain, which is incorrect. We are left with option C. which makes sense because oxygen is needed to form carbon dioxide and water, and is also used in oxidative phosphorylation.


So my question: Is the oxygen provided by RBCs really required in Kreb Cycle. I haven't scrutinized the biochemistry of the Kreb Cycle (yet), but it seemed to me that the O2 was not directly required. I poked around and found that Sparknotes says, "Though the Krebs cycle does not directly require oxygen, it can only take place when oxygen is present because it relies on by-products from the electron transport chain, which requires oxygen".

So someone is wrong either way... Anyhow, I thought O2 provided by RBC was only necessary as the final electron acceptor for the ETC, which is why I answered D...

Any pros?

 

[Vihsadas]

Which of the following biological processes will be most affected by the presence of the mutant gene for sickle cell anemia in an individual?

A. Fermentation of pyruvate to lactate and ATP
B. Production of pyruvate and ATP in glycolysis
C. The production of carbon dioxide, water and ATP during the Kreb's cycle and oxidative phosphorylation
D. The production of carbon dioxide and ATP from ADP in the electron transport chain


Explanation
Corrent Answer: C

Sickle cell anemia lowers the oxygen-carrying capacity of red blood cells. This means that less oxygen is reaching the cells for use in cellular respiration. Fermentation of pyruvate to lactate and ATP will occur in the absence of oxygen, which is not the case here. Glycolysis occurs whether oxygen is present or not, so this process will also be unaffected. Option D. states that carbon dioxide is produced through the processes of the Electron Transport Chain, which is incorrect. We are left with option C. which makes sense because oxygen is needed to form carbon dioxide and water, and is also used in oxidative phosphorylation.


So my question: Is the oxygen provided by RBCs really required in Kreb Cycle. I haven't scrutinized the biochemistry of the Kreb Cycle (yet), but it seemed to me that the O2 was not directly required. I poked around and found that Sparknotes says, "Though the Krebs cycle does not directly require oxygen, it can only take place when oxygen is present because it relies on by-products from the electron transport chain, which requires oxygen".

So someone is wrong either way... Anyhow, I thought O2 provided by RBC was only necessary as the final electron acceptor for the ETC, which is why I answered D...

Any pros?

Okay, you're thinking about this in the right way, and you're almost putting all the pieces together. First of all, C is definitely the right answer. Try and think of this problem in terms of downstream effects, i.e. glycolysis produces pyruvate which is needed in the TCA, etc., etc.

So, while O2 is not directly needed in the TCA, the continuation of the TCA is directly dependent on if the electron transport chain is active or not. If the ETC cannot function, the TCA will stop.

So, I think you've already got a good handle on why A and B are wrong, so I'll leave those alone.

D. Without fully understanding what is going on, you should still be able to eliminate this answer because CO2 is simply not produced in the ETC. It is produced in the TCA, but the question explicity states "CO2 production in the ETC." So it HAS to be wrong.

But let's look at why "C" is definitely right.

So, all of CO2, ATP and Water are produced in the TCA. So that part at least is fine. Now, what happens if you don't have oxygen? Well, the ETC will stop functioning, so that means that the TCA will be backed up, and it will stop functioning too. So it will stop producing Water, ATP and CO2. And that's what the question is asking about: the production of water CO2 and ATP.

Now, it is true that the ETC requires O2 as well. But look at how choice D is worded. It is just asking about the "production of CO2 in the ETC" not about the ETC in general. So because CO2 is not produced in the ETC, the production of CO2 by the ETC cannot be affected by a decrease in O2. The ETC itself, however, can.

So the trick is in realizing that although BOTH the TCA and the ETC are dependent on O2, the ETC does not produce carbon dioxide. Therefore, since the answer choice is asking about "carbon dioxide production in the ETC", it can't be correct.

I hope this helps.

 

[andafoo]

Okay, you're thinking about this in the right way, and you're almost putting all the pieces together. First of all, C is definitely the right answer. Try and think of this problem in terms of downstream effects, i.e. glycolysis produces pyruvate which is needed in the TCA, etc., etc.

So, while O2 is not directly needed in the TCA, the continuation of the TCA is directly dependent on if the electron transport chain is active or not. If the ETC cannot function, the TCA will stop.

So, I think you've already got a good handle on why A and B are wrong, so I'll leave those alone.

D. Without fully understanding what is going on, you should still be able to eliminate this answer because CO2 is simply not produced in the ETC. It is produced in the TCA, but the question explicity states "CO2 production in the ETC." So it HAS to be wrong.

But let's look at why "C" is definitely right.

So, all of CO2, ATP and Water are produced in the TCA. So that part at least is fine. Now, what happens if you don't have oxygen? Well, the ETC will stop functioning, so that means that the TCA will be backed up, and it will stop functioning too. So it will stop producing Water, ATP and CO2. And that's what the question is asking about: the production of water CO2 and ATP.

Now, it is true that the ETC requires O2 as well. But look at how choice D is worded. It is just asking about the "production of CO2 in the ETC" not about the ETC in general. So because CO2 is not produced in the ETC, the production of CO2 by the ETC cannot be affected by a decrease in O2. The ETC itself, however, can.

So the trick is in realizing that although BOTH the TCA and the ETC are dependent on O2, the ETC does not produce carbon dioxide. Therefore, since the answer choice is asking about "carbon dioxide production in the ETC", it can't be correct.

I hope this helps.

Haha, I was reading another post you answered about glycolysis and acidosis. I can see why D is wrong, only water forms as a result of the ETC. And if I get you fully, Krebs cycle does not ever require O2, I believe it gets its full share of oxygen from CO2 and maybe a lone water somewhere. But the effect TCA experiences is a consequence of the primary effect on the ETC. Thus, C is the only accurate statement.

Thanks!