NADH and FADH2

[TLL]

Princeton Review says NADH yields on avg 2.5 ATP; FADH2 1.5 ATP

Kaplan says: 3 for NADH and 2 for FADH2.

Which one will be right on the AAMC?

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[mcatbeast]

id go with the one that says 3 ATP for NADH and 2 ATP for every FADH2. i doubt your gonna get a discrete that asks that directly, its better to know overall how many NADH and FADH2 are produced where and during what stage and overall how many net atp are produced.

GLYCOLYSIS: 2 NET ATP per glucose
PDC: 2 NADH per pyruvate
CAC: 1 GTP , 3 NADH , 1 FADH2 (happens twice per glucose molecule)

hope that helps

 

[ilovemcat]

Princeton Review says NADH yields on avg 2.5 ATP; FADH2 1.5 ATP

Kaplan says: 3 for NADH and 2 for FADH2.

Which one will be right on the AAMC?

Well first - What is NADH? It's an electron carrier. NADH releases its 2 electrons into the Electron Transport Chain. These 2 electrons pass through all 5 electron carriers. Everytime an electron passes through an electron carrier, 1 Proton is pumped from the Matrix to the intermembrane space. Because there are 2 electrons and they are passed in total 5 times, 10 Protons are pumped through per NADH.

Now that I explained that - how do you make ATP? Remember those protons I mentioned? The very unfavorable production of ATP is driven by the pumping of protons into the Matrix.

To phosphorylate ADP + Pi -> ATP requires the pumping of 3 Protons. However, 1 Proton is needed to transport Cytosolic Pi into the Mitrochondrial Matrix. Therefore, 4 Protons are "used up" per ATP molecule created.

Since each NADH yields 10 Protons - 5 ATP molecules are created per 2 NADH (or 2.5 ATP per).

FADH2 doesn't release its electrons to the first carrier of the ETC (NADH Dehydrogenase). Instead it releases its electrons to the ETC carrier, Ubiquione. As a result, it yields a total of 6 Protons per FADH and ultimately results in the creation of 3 ATP molecules per 2 FADH or (1.5 ATP per).

This is what I learned. However, the reason why theres so much discrepency as to how much ATP is produced is because no one is really sure how many protons are actually used to create ATP. It's all theoretical. This also accounts for the differences in actual values of ATP produced per oxidation of a Glucose molecule. Some sources say 30 (Eukaroytes) and 32 (Prokaryotes). Others say 36 and 38 respectively. It's unlikely MCAT writers will throw both numbers at you - but either one can show up in a multiple choice question.

 

[t1me]

"Estimates of the number of protons required to synthesize one ATP have ranged from three to four,[65][66] with some suggesting cells can vary this ratio, to suit different conditions.[67]"
http://en.wikipedia.org/wiki/Oxidative_phosphorylation#ATP_synthase_.28complex_V.29

That being said, it seems the general consensus that the "theoretical yield" is 36/38 ATP, meaning 3H+ per ATP, meaning 3ATP per NADH and 2ATP per FADH.
http://en.wikipedia.org/wiki/Cellular_respiration#Theoretical_yields

The AAMC is about the "big picture" and application of "simple scientific principles". I would think that you take the simpler approach of the two and go with the number without decimals. This is just my opinion, however, because ilovemcat's post is 100% correct. I just don't know if the AAMC is THAT anal to consider the proton used to transport Pi.

 

[docelh]

Princeton Review says NADH yields on avg 2.5 ATP; FADH2 1.5 ATP

Kaplan says: 3 for NADH and 2 for FADH2.

Which one will be right on the AAMC?

Both counts are built on different assumptions that factor in external processes. The important thing is that NADH will yield more net ATP than FADH b/c it enters the ETC earlier.