Nov 6, 2019
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  1. Pre-Medical
In Berkeley Review it uses the statement, "Consequently, if we utilize the malate-aspartate shuttle, the 2 NADHs from glycosis will give us 6 ATPs while the 8 NADHs from the Krebs Cycle will give us 24 ATPs." Are they making the assumption that the Krebs Cycle and the malate aspartate shuttle are both in the Krebs Cycle. Otherwise, wouldn't the Krebs Cycle only give 18 ATP for the 6 NADH produced (1 NADH = 3 ATP; 1 FADH2 = 2 ATP), while the other 6 ATP comes from the 2 NADH produced in the Malate Phosphate shuttle (it says 1 NADH = 3 ATP for the Malate Asparate Shuttle versus the alternative 1NADH = 2 ATP for the Glycerol Phosphate Shuttle)? I remember learning that the shuttles are separate from the Krebs Cycle (I also remember there being another general term used for the shuttling process to the Krebs Cycle). Is that correct?

Also, does anyone know if the mitochondrial DNA contains genes for all the ETC proteins and the ATPase?

Also, for glycolysis steps that don't involve ATP input with a large delta G positive value (nonspontaneous), how do they proceed forward? I understand that enzymes will reduce the activation energy, but will not change the energies of the initial and final states. For example, step 4 of glycolysis with aldolase and Fructose 1,6-Diphosphate to Glyceraldehyde-3-phosphate.

Another question I had was with the Fatty Acid Oxidation total ATP gained, where it says from beta-oxidation of palmitic acid (C16 fatty acid), then after 8 of the acetyl-CoA enter the Krebs Cycle, they produce 3 NADH and 1 FADH2 and 1 GTP per acetyl-CoA. Could someone clarify how the Acetyl-CoA entering the Krebs Cycle results in those NADH, FADH2, and GTP numbers? Thank you.

Edit: I added a few questions in edits, prior to any responses. I would be happy with answers to all or any of the above questions in replies.
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Hi. Some of this is out of scope.

# of ATP in this context - don't worry about it. Why?

NADH+H+ and ATP : FADH2 ratios during the oxidative phosphorylation appear to be not 3 and 2, but ~2.5 and ~1.5 respectively. Unlike in the substrate-level phosphorylation, the stoichiometry here is difficult to establish. It's not going to be explicitly tested on the MCAT; even if it were, I'd cut my losses with such a question and move on.

When delta naught is largely positive, end product concentrations can still facilitate flux if they are removed from the system i.e. remove end product build up to lower the value of ln Q where Q is [products]/[reactants]. Thermodynamics here are not static.

Shuttles and Krebs are not separate, products of the shuttles directly influence Krebs. Malate, aspartate, phosphate concentrations affect both and they are always connected.

Re: ACoA metabolism, again don't dwell over the stoichiometry.

Good luck!


2+ Year Member
Dec 5, 2017
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  1. Pre-Medical
There were questions like that which felt too detailed in terms of what they expected you to know. They frustrated me to no end when I was studying. Rest assured that the MCAT passages will give you all of those details and will be clearer when asking for what you need to consider. Know the concept and how to reason through the material, rather than worrying about recalling the material. Camioxu makes an excellent point about seeing the big picture and not the stoichiometry details.

The strength of their science books lies in learning to reason and connect the dots between seemingly different subjects. Get your reasoning down and don't get overwhelmed by the details.
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