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H+ in Glycolysis/CAC

Discussion in 'MCAT Study Question Q&A' started by nothing123, May 25, 2008.

  1. nothing123

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    Hi,

    I never really figured out where the 2H+ and the 4H+ in the products of glycolysis and CAC respectively come from. Anybody know?

    Thanks.
     
  2. Vihsadas

    Vihsadas No summer
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    Remember that the fluids in the body are constantly buffered in terms of pH. So, for the purposes of biochemical reactions you can assume that protons and hydroxyl ions are plentiful. You don't need to worry about where exactly they come from, but most likely come from the Carbon dioxide equilibrium with Carbonic Acid, Bicarbonate and Carbonic Anhydrase enzyme.
     
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    nothing123

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    Hmm, my question wasn't so much what is the source of the protons but what they're actually doing there (i.e. how did they just show up in the products). Is it from the NAD+ + H+ --> NADH + H+ reaction? Why does NAD+ have to react with two hydrogen protons anyways?

    Thanks.
     
  4. rocuronium

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    I found this on the Wikipedia site for NAD+:

    In metabolism the compound accepts or donates electrons in redox reactions. Such reactions (summarized in formula below) involve the removal of two hydrogen atoms from the reactant (R), in the form of a hydride ion, and a proton (H+). The proton is released into solution, while the reductant RH2 is oxidized and NAD+ reduced to NADH by transfer of the hydride to the nicotinamide ring.

    RH2 + NAD+ → NADH + H+ + R
     
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    nothing123

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    Great thanks, that pretty much answered my question. In the Krebs cycle alone, the number of H+ produced should be 3 then (per acetyl-CoA) since 3 NADH are produced? I don't know why my Princeton book says 4...
     
  6. rocuronium

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    I believe that is correct, unless it is including the H+ produced with NADH by the pyruvate dehydrogenase complex to produce the acetyl-CoA.
     
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  7. Vihsadas

    Vihsadas No summer
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    :thumbup: That's where it comes from. There's a semantical argument however that the PDH enzyme is not part of the CAC. Meh, who knows. :p
     
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