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Energetics of Glucose Catabolism

Discussion in 'MCAT: Medical College Admissions Test' started by GoldenSword, Feb 26, 2007.

  1. GoldenSword

    2+ Year Member

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    ok, I'm really confused on this topic w/ 3 different sources,

    1-TPR: 2.5 ATPs per NADH
    ..........1.5 ATPs per FADH2
    total for Eukaryotic aerobic resp: 30
    total for Prokarytic aerobic resp: 32

    2-EK: 3 ATPs per NADH
    ........2 ATPs per FADH2
    total for Eukaryotic aerobic resp: 36
    total for Prokaryotic aerobic resp: 38

    3-My Biochem teacher: something close to EK, but I end up w/ 38 ATPs for Eukaryotic and 40 for Prokaryotic :laugh:

    Clarification please, me very very confused, DAMN it....LOL
     
  2. turquoise_water

    turquoise_water Junior Member
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    oh boy 40 ATPs for Prokaryotes :laugh: :laugh: :laugh: :laugh:

    ok coming back to your question ....

    In Glycolysis, there is net gain of 2 ATPs, + 2 NADH

    Pyruvate Decarboxylation yields 1 NADH for each pyruvate molecule. We have 2 pyruvates from Glycolysis, therefore, 2 NADH gain from here .

    Now we move to Kreb Cycle , for each pyruvate you get 1 ATP, 3 NADH, 1 FADH2 (the way i remember it is 1:3:1 ) . We have 2 pyruvates, therefore its going to be.... 2 ATPs , 6 NADH , 2 FADH2

    now comes the Electron Tranport .... where each NADH produces 3 ATP, and each FADH2 produces 2 ATPs ....

    The most important thing to remember here is that the 2 NADHs we got from Glycolysis DONT enter mitochondria and dont participate in ETC, therefore they yield 2 ATP each and not 3

    Now if u calculate the TOTAL ATPs .... you get 36 :D

    * 2 ATP - Glysolysis
    * 4 ATP - from 2 NADH produced by glycolysis
    * 6 ATP - from pyruvate decarboxylation
    * 2 ATP, 18 ATP (from 6 NADH), 4 ATP (from 2 FADH2) - Kreb Cycle

    Hope this helped :)
     
  3. OP
    OP
    GoldenSword

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    Thanks a lot, now it makes sense. This is just what EK was explaining and I just didn't understand their calculation.
    :thumbup:
     
  4. cookiegurl

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    Okay, I think I definitely learned it differently than turquoise_water. All of this information is in Lehninger's Principles of Biochemistry btw if you want to check it out.

    Glycolysis (Glucose --> 2 pyruvate)
    4 ATP and 2 NADH per glucose molecule (2 substrate level phosphorylation to form each pyruvate)

    Pyruvate Dehydrogenase Complex (pyruvate --> acetyl CoA)
    2 NADH (Enzyme 3)

    Krebs Cycle (oxidation of acetyl CoA --> CO2)
    2 GTP/ATP, 6 NADH, 2 FADH2

    NADH = 2.5 ATP
    FADH2 = 1.5 ATP

    So, total
    NADH = 10 x 2.5 = 25 ATP
    FADH2 = 2 x 1.5 = 3 ATP
    4 ATP (glycolysis) = 4 ATP

    Total: 32 ATP max
    It should be 34 ATP if you include the GTP/ATP formed during Krebs Cycle-- but you also did use 2 ATP during the Prep phase of Glycolysis.

    But, you can make 30 ATP also

    How? This is due to the mechanism that transports the NADH from the cytosol (formed during glycolysis) to the mitochondria.

    If you use the Aspartate/Malate Shuttle, the NADH actually enters the mitochrondria and is used to form ATP but if you use Glycerol 3 (P) Dehydrogenase to directly transfer NADH's electrons to FAD in Complex II (ETC), you do not make ATP with them.

    The short reason why is that ATP synthesis is directly related to the # of H+ being pumped out across the membrane. In Complex II (the method using Glycerol 3 (P)) of ETC, NO H+ is pumped out during electron transfer. Thus, less protons = less ATP, and therefore, the reason for the ATP range.

    Hope I didn't make this overly complicated (or messed up on a part!!) :)

    Good luck with studying
     

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