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question concerning KREB cycle

Discussion in 'NBDE Exams & Licensure Exams' started by dentheartthrob, May 13, 2007.

  1. dentheartthrob

    dentheartthrob DreamDMDweaver 10+ Year Member

    421
    10
    Apr 14, 2005
    hi, i have doubts form the two review materials that I am studying from. NBDE first Aid says that there is a total of 8 NADH formed during the TCA cycle, while the one written on USMLE first aid says 6 NADH are formed, I've checked wikipedia and, information written on USMLE seemed to be accurate, but after adding up all the total ATPs produced from the three metabolic pathways (glycolysis, TCA, and ETC) the sum written on the NBDE first aid is more accurate (36-38atp)....Can someone be nice enough to explain this to me? Is there a typographical error or am i missing something?...Thanks
     
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  3. Prosthoman

    Prosthoman Banned Banned

    241
    1
    May 29, 2006
    both are true, it depends on the pathway, remember kreb cycle, I think in the middle of it, things can go two ways, one needs to spend another 2 NADH I remember, or something like that, so the end product is 36 rather than 38. However, if the alternate path goes, then that 2 ATP is saved and the end product is 38. So, both are correct, however if you see both choises, answer is 38
    read this please: or visit this page:
    Frequently 36 ATP are quoted because it is known that in eukaryotic cells that the reduced NAD formed by glycolysis in the cytoplasm must be actively transported across the mitochondrial membrane to be made available to the electron transport chain. The cost of such active transport is one ATP for each NADH transported. Thus, the net gain for each cytoplasmic NADH is only two ATP rather than three. However if one plays this game, then one should also consider the active transport of other molecules as well (pyruvate? phosphate? Mg++? etc.). The actual net gain of ATP is unknown but must be regarded as less than 36.
    In eukaryotic cells the Kreb's cycle occurs in the liquid part of the mitochondria (matrix) while the electron transport chain occurs in the inner membrane (cristae).
    http://www.mrs.umn.edu/~goochv/CellBio/lectures/kreb/kreb.html
    I hope this helps
    good luck to you
     

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