Aerobic Respiration

[MedPR]

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Need the highlights please.

Glycolysis is anaerobic and yields 2 net ATP. Two pyruvate per glucose enter the TCA cycle.

Is the electron transport chain part of the TCA cycle? Is it a subsequent step (like TCA is subsequent to glycolysis)?

I understand (I think) how each process works, but I don't really get how they are interconnected.

When we talk about 36 net ATP, does that mean that the TCA cycle nets 34 ATP, or that the electron transport chain nets 34 ATP? Or TCA + ETC = 34ATP?

When I think about it, the only thing I actually know is this.

Glucose ----> Glycolysis ---> 2 ATP + 2 Pyruvate -----> TCA ---> 34 ATP.

Help please!

 

[chiddler]

Electron transport chain and chemiosmotic ATP generation are usually lumped together. So ETC is distinct from TCA cycle. This is because ETC occurs around the inner mitochondrial membrane while the TCA occurs within the mitochondrial matrix. They are connected just like how glycolysis and TCA are connected: glycolysis provides pyruvate for the TCA to progress. Similarly, the ETC requires NADH and FADH2 to progress which is supplied from TCA and glycolysis.

Wait, in my book and my notes I have the following:

Bacteria net 32 ATP and eukaryotes net 30. The reason for this difference is eu's have to use glycerol phosphate shuttle to get the glycolysis NADH inside which takes ATP so the net is reduced a bit.

So, please correct me if i'm wrong, but i think your numbers are gross ATP produced.

edit: what the hell. why does my book say 30-32 atp. rereading...

"These numbers reflect the most recent understanding of ATP synthesis, and as such, may not appear in some textbooks that still cling to the previously established counts of 36 ATP per glucose in eukaryotes and 38 ATP per glucose in prokaryotes."

heh. now that i think about it, i remember these numbers from high school biology...

 

[SaintJude]

Yes, Glycolysis is Anaerobic and Nets 2 ATP
We lose 2 ATP molecules in pyruvate decarboxylation

Sometimes TCA + e-chain considered by its "nature" as a single aerobic component, while other times it is divided according to location.
TCA cycle nets : 2 ATP . Occurs in Mitochondrial Matrix
Electron transport chain nets: 34 ATP. Occurs in Inner Mitochondrial Membrane

You're right in in making a distinction between energy outputs of TCA and electron transport chaing, because quite a few people sometimes forget that the citric acid cycle does not directly generate much energy. This makes sense if one understands the purpose of the TCA cycle. The value of the TCA cycle is that it generates high-energy electrons that are carried by NADH and FADH2.

 

[MT Headed]

Also remember that glycolysis ends with pyruvate, but TCA cycle starts with an input of acetyl-CoA. So there is a step where pyruvate gets converted to acetyl-CoA as well. Know both where this reaction occurs, and what kind of energy molecule gets kicked off during this process.

Because this reaction is so neglected, it is ripe for an mcat BS passage topic.

 

[MedPR]

Thanks everyone 🙂

Also remember that glycolysis ends with pyruvate, but TCA cycle starts with an input of acetyl-CoA. So there is a step where pyruvate gets converted to acetyl-CoA as well. Know both where this reaction occurs, and what kind of energy molecule gets kicked off during this process.

Because this reaction is so neglected, it is ripe for an mcat BS passage topic.

I certainly do remember that this reaction occurs between glycolysis and TCA, but where does it occur? And what do you mean what kind of energy molecule?

I thought the pyruvate was just oxidized into CO2 + acetyl-CoA?

 

[chiddler]

Thanks everyone 🙂




I certainly do remember that this reaction occurs between glycolysis and TCA, but where does it occur? And what do you mean what kind of energy molecule?

I thought the pyruvate was just oxidized into CO2 + acetyl-CoA?

It occurs inside mitochondria. NAD is also reduced.

 

[mcloaf]

The old pyruvate dehydrogenase complex. It's actually a pretty awesome enzyme, if you're into that sort of thing. 🙂

 

[MedPR]

It occurs inside mitochondria. NAD is also reduced.

so NAD+ is reduced to NADH to make acetyl-CoA.

Aren't NADH and FADH2 initial electron acceptors? But wouldn't that mean they are reduced also?

 

[chiddler]

so NAD+ is reduced to NADH to make acetyl-CoA.

Aren't NADH and FADH2 initial electron acceptors? But wouldn't that mean they are reduced also?

Yeah the entire reaction is NAD+ to NADH, CO2 emitted, and acetyl-SH attached to make acetyl CoA.

NAD+ and FAD++ are electron acceptors. NADH and FADH2 is their reduced form. Sorry can you please explain what you're asking i'm not sure I understand.