Cellular Respiration ATP Yield

[DentalNucleicAcid]

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I'm confused about how exactly Eukaryotes "spend" 2 ATP during cellular respiration and as a result net 36 ATP rather than 38 ATP like Prokaryotes do. I've checked Feralis notes and questions posted on this forum and they say that it costs 2 ATP to move the 2 pyruvates from the cytosol into the mitochondrial matrix. This makes sense, but I thought the 2 ATP are used during glycolysis itself. What I mean is, the first ATP that is spent is used to phosphorylate glucose to glucose-6-phosphate. The second ATP that is spent is used to phosphorylate fructose-6-phosphate to fructose-1,6-bisphosphate. And there goes the 2 ATP. In other words, the 2 ATP are used during glycolysis, before pyruvate is made, right? But the sources suggest that they're used after glycolysis, to shuttle the pyruvate by active transport. Can someone please clarify? Thanks

 

[rdub]

2 ATP are indeed invested in glycolysis, but then 4 ATP are produced in glycolysis. This means that overall, we did not spend 2 ATP during glycolysis, but we actually gained 2 (so do not think about it as spending 2 ATP, but rather investing 2 ATP). After glycolysis + the citric acid cycle + the electron transport chain we are left with a net gain of 38 ATP. It then takes 2 ATP to move NADH across the mitochondrial membrane so we end up with 36.

 

[DentalNucleicAcid]

2 ATP are indeed invested in glycolysis, but then 4 ATP are produced in glycolysis. This means that overall, we did not spend 2 ATP during glycolysis, but we actually gained 2 (so do not think about it as spending 2 ATP, but rather investing 2 ATP). After glycolysis + the citric acid cycle + the electron transport chain we are left with a net gain of 38 ATP. It then takes 2 ATP to move NADH across the mitochondrial membrane so we end up with 36.

So you're saying that cellular respiration in eukaryotes actually consumes 4 ATP altogether? As in, 2 ATP are used to phosphorylate glucose during glycolysis, and another 2 ATP are used to transport NADH into the mitochondrial matrix? Because this fact isn't usually stated very clearly but it makes complete sense. This is where my confusion came from.

You also brought up another topic that I'm unclear about. The 2 ATP that are used to transport NADH into the mitochondrial matrix, are used to transport NADH, correct? Not pyruvate? Because I understand that both NADH and pyruvate need to enter the mitochondrial matrix for use in the electron transport chain and krebs cycle, respectively. So which one requires the 2 ATP?

 

[rdub]

So you're saying that cellular respiration in eukaryotes actually consumes 4 ATP altogether? As in, 2 ATP are used to phosphorylate glucose during glycolysis, and another 2 ATP are used to transport NADH into the mitochondrial matrix? Because this fact isn't usually stated very clearly but it makes complete sense. This is where my confusion came from.

You also brought up another topic that I'm unclear about. The 2 ATP that are used to transport NADH into the mitochondrial matrix, are used to transport NADH, correct? Not pyruvate? Because I understand that both NADH and pyruvate need to enter the mitochondrial matrix for use in the electron transport chain and krebs cycle, respectively. So which one requires the 2 ATP?

Yes, from what I understand a total of 4 ATP is consumed altogether. Depending on how technical you want to get, I don't know if it is accurate to say that the two ATP consumed to transport NADH occurs in cellular respiration. I think technically it is after cellular respiration. But I doubt it really matters...

As far as your question on NADH vs Pyruvate...read this from Cliffs APBio:

 

[DentalNucleicAcid]

Yes, from what I understand a total of 4 ATP is consumed altogether. Depending on how technical you want to get, I don't know if it is accurate to say that the two ATP consumed to transport NADH occurs in cellular respiration. I think technically it is after cellular respiration. But I doubt it really matters...

As far as your question on NADH vs Pyruvate...read this from Cliffs APBio:

Awesome, thank you. I'll stick with the 2 ATP being used in NADH transport then.