# After glycolysis in humans, where has most of the energy gone?

1. Jun 24, 2005

### student007

After glycolysis in humans, where has most of the energy gone?

I'm confused because i know that ATp is a high energy molecule, but NADH holds high energy electrons, and pyruvate holds much of the free energy that was previously present in the bonds of the glucose molecule.

2. Jun 24, 2005

### quetzalcoatl9

well, each NADH is equal to around 3 ATPs, and FADH2 is around 2 ATPs.

once pyruvate gets fed into the TCA cycle, there will be tons of reduced NAD and FAD around, which will power oxidative phosphorylation which in turn will boost ATP output to around 32 ATPs instead of the measley 2 net ATPs that you get out of glycolysis.

so i say: pyruvate.

3. Jun 30, 2005

### pattylou

Glycolysis is only the first step in glucose catabolism. I assume you have a textbook handy? There are three stages in our mitochondria, in the breakdown of a sugar molecule to produce ATP. Those stages are glycolysis, Krebs/TCA, electron transport.

Look at the whole three-stage process. Glycolysis is the first stage - most of the energy hasn't been released yet. Where is it? (You can figure that out from the figure of glycolysis in your text.) Figure that out and you have your answer.

4. Jun 30, 2005

### quasi426

Glycolysis yields 2 ATP (energy molecules) per glucose molecule broken down into 2 pyruvates. So after glycolysis we still have energy conserved in the 2 pyruvate molecules which, as described above by other forum patrons will can be eventually converted to 32 ATPs or so.

I'll digress a little just to talk about why we have evolved to use ATP instead of just using the other higher energy molecules. My metabolic instructor Professor Hampton put it like this, " ATP is the twenty dollar bill of the cell." This analogy is trying to convey that many processes in the cell can use the energy of ATP since it is in useable dosages. This leads to higher effieciency.

5. Jul 1, 2005

### quetzalcoatl9

that really doesn't answer your question though...why not store the energy as high-energy thiol bonds, for example? why the ATP molecule?

i suspect that maybe the answer has to do with the fact that ATP is easily hydrolyzed (you need nothing more than water to get the energy out of ATP), so you get a $$\Delta G = -30.5kJ$$ with little activation energy.

as for it's universality, most enzymes are activated/deactivated by phosphorylation, so having ATP as the energy molecule allows for regulation of pathways by the amount of free energy in the cell.

6. Jul 5, 2005

### quasi426

The claim you made above indicates that you do not understand evolution and natural selection. Why do you think that most enzymes are activataed/deactivated by ATP? Organisms evolved proteins that use ATP for functions such as protein-protein communication and switches did so because ATP was very plentiful. Proteins did not evolve their ability to use ATP for signaling purposes before the cell was flooded with ATP. So there is no reason to state "as for its universality."

To conserve energy it is better to only use what is needed. So if I only need a stick of dynamite to blow something up, there is no need to use a nuclear bomb.

7. Jul 5, 2005

### quetzalcoatl9

Thank you for the lecture, professor. Having studied the AKT and PKC pathways in human brain cells for years, I happen to know a thing or two about cell signaling. I never said that the cell "was flooded with ATP", where did you get that from?

My point was that ATP plays a role in things other than just energy production.

And where is the "nuclear bomb", professor? A thiol bond? Can you tell me the $\Delta G$ for the hydrolysis of the acetyl-CoA thiol bond?

I was not implying that nature is imperfect, only difficult for our human minds to understand. Eurkaryotic metabolism is only ~50% effecient, better than your car but worse than electrical energy conversion. However, this ineffeciency serves an important purpose.

8. Jul 6, 2005

### quasi426

The reason I gave the nuclear bomb and dynamite analogy was an extreme analogy to show what I meant. I got from your post was that you implied that ATP is so abundant partly due to its role in signal transduction, and I was just saying that signal transduction evolved its use of ATP in its system (kinases post-translational modifications) because it was plentiful. Also sorry if my tone was slightly condescending.