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TPR Free Online Exam BS Question #14

Discussion in 'MCAT Study Question Q&A' started by dancerdoc89, Aug 16, 2011.

  1. dancerdoc89

    dancerdoc89 Knowledge is Power

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    Can you please clarify the concepts presented in this question (it is question #14):

    During strenuous physical exertion, muscle tissues switch from aerobic to anaerobic metabolism. The net products per glucose molecule under these conditions are:

    A. 4 ATP, 2 NADH, 2 lactic acid
    B. 4 ATP, 2 NADH, 2 pyruvate
    C. 2 ATP, 2 NAD+, 2 lactic acid
    D. 2 ATP, 2 NAD+, 2 pyruvate

    Ok, so I believe glycolysis and lactic acid fermentation are the only two pathways we should be concerned with. Glycolysis yields a net of 2 ATP, 2 NADH, and 2 pyruvate. Lactic acid fermentation utilized these 2 pyruvate and oxidizes the 2 NADH to 2 NAD+. However, don't we get ATP (2 ATP per glucose) via lactic acid fermentation? Shouldn't that be a total net of 4 ATP, 2 NAD+, 2 lactic acid?

    Thanks for your help.
     
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  3. FutureDoctor503

    FutureDoctor503 A.W.E.S.O.M.-O
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    ATP is not produced during lactic acid fermentation, only 2 NAD+ are produced for another cycle of glycolysis.
     
  4. dancerdoc89

    dancerdoc89 Knowledge is Power

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    I'm assuming the same for ethanol fermentation...
     
  5. dorjiako

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    Anaerobic respiration which is the question includes both glycolysis and fermentation. Glycolysis yields 2ATP, 2 NADH and 2 PYRUVATE. Since the 2 pyruvate and the 2 NADH are oxidized to 2 NAD+ and 2 Lactic acid during fermentation (which is part of anaerobic respiration), the net result is then 2ATP, 2NAD+ and 2 lactic acid.
    Hope this helped.
     
  6. MT Headed

    MT Headed snow, PBR, and bears
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    Can you really claim that anaerobic metabolism produces a net of NAD+? Wasn't NAD+ used up during glycolysis to produce NADH?

    This sounds like a lousy question.
     
  7. liveoak

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    NADH is used as a reducing agent to reduce pyruvate into lactic acid.

    Thus, NADH is oxidized back to NAD+
     
  8. MT Headed

    MT Headed snow, PBR, and bears
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    But claiming that the process produces a net of NAD+ makes about as much sense as me putting a feather on a pig, taking the feather off of the pig, and claiming that my process produced a net of one pig.
     
  9. geeyouknit

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    ATP is produced.
    1 glucose molecule net produces 2 ATP, 2 NADH (2 NAD+ molecules are reduced to NADH), and pyruvate.
    To get back NAD+ for future glycolysis, pyruvate becomes lactate and 2x NADH --> 2x NAD+.

    It's net 2 ATP, because 4 ATP is produced, but 2 ATP is used up in the glycolysis process.
     
  10. dancerdoc89

    dancerdoc89 Knowledge is Power

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    yes, it did help, thanks. thanks to the other posters, too...I always thought "anaerobic metabolism" = fermentation. but turns out it = glycolysis + fermentation...

    ...btw, I thought fermentation in itself produced 2 ATP per glucose (or, per 2 pyruvate)....Kaplan straight out said that, too...unless Kaplan meant fermentation as collectively meaning glycolysis + fermentation (as glycolysis is needed to get to the fermentation step).

    Thanks! :thumbup:
     
  11. paul411

    paul411 ANES
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    Edit: nvm.
     

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