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CO binding

Discussion in 'MCAT Study Question Q&A' started by Deepa100, May 17, 2008.

  1. Deepa100

    Deepa100 Junior Member
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    CO poisoning damages cells by:
    A. uncoupling ATP production and the mitochondrial protein gradient.
    B. inhibition of the Krebs cycle.
    C. inhibitng fermentation to lactate.
    D. inhibiting glycolysis.

    Correct Ans:B
    Why?
     
  2. RPedigo

    Physician Faculty Moderator Emeritus 10+ Year Member

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    If you inhale carbon monoxide what happens to oxygen transport?

    If you are out of oxygen, are you going to do aerobic or anaerobic respiration?

    Which pathway is inhibited?
     
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  3. tncekm

    tncekm MS-1
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    Yeah, that's what I was thinking. But, the oxygen specifically acts as an electron acceptor at the inner mitochondrial membrane. So I'm having trouble seeing exactly how the Krebs cycle is being inhibited. The only thing I can think of is that b/c there is no oxygen to accept electrons, you will get a buildup of Krebs cycle products and it will be inhibited, but I just don't feel satisfied with that, personally.
     
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  4. RPedigo

    Physician Faculty Moderator Emeritus 10+ Year Member

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    Right, but the other answers are completely false, making B the best answer choice. It's the "least wrong" answer, I guess.

    A. It cannot be A because CO is not an uncoupling agent. An uncoupling agent allows the protons pumped into the intermembrane space to flow back into the matrix through somewhere other than ATP synthase. That is, the electron transport chain keeps chugging, but makes much less or no ATP. 2,4-DNP is a mitochondrial uncoupling agent.

    B. This is the correct choice, for reasons that tncekm said.

    C. Once anaerobic respiration began, the opposite would be true. Gotta regenerate that NAD+ somehow.

    D. No, glycolysis can occur in the absence of oxygen.
     
  5. Deepa100

    Deepa100 Junior Member
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    And we could give the same reasoning for the glycolysis option too, that too much products build up, no?
     
  6. RPedigo

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    What products of glycolysis would build up? You'd undergo lactic acid fermentation to regenerate NAD+ and you'd just keep chugging along making a small amount of ATP via glycolysis since you don't have oxygen.
     
  7. tncekm

    tncekm MS-1
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    *sigh* I hate "least wrong" answers. They're so frustrating.
     
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  8. RPedigo

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    Agreed :(

    However, elimination of answers is how I got through confusing questions on the MCAT that tested topics that I didn't understand fully. Often times I eliminate all other answers, rather than choose one. I find that choosing the "correct" answer often makes people fall into traps, so by eliminating all other choices with sound reasoning, you're usually good to go.
     
  9. tncekm

    tncekm MS-1
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    Yeah, I've learned the hard way that I definitely need to look at every single answer seriously. Especially in those cases where you get an easy calculation that provides both the correct answer, and the answer that's very easy to make when you incorrectly distribute factors of 10! (i.e. 3.6*10^10/1.2*10^-2 = 3 * 10^12, but they'll off you a 3*10^8 just in case you slip up!)
     
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  10. Vihsadas

    Vihsadas No summer
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    Like Cyanide, Carbon Monoxide directly inhibits complex IV of the Electron transport chain.
    Thus, you'll get a buildup of NADH and FADH2 from the action of the TCA cycle, and eventually a build up of intermediates will cause the TCA to shut down. Glycolysis will then take over.
     
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  11. Deepa100

    Deepa100 Junior Member
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    Yep, got it. Thx!
     

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