Thread: Consumption of glucose

I also have done some university studies in this area, and here is my understanding.

The first source of energy is ATP and creatine phosphate (phosphocreatine). These two things combined make up the phosphagen system, which is what you use when you lift weights or jump or run quick sprints. There is enough of these stored in muscles to contract for about 10 seconds.

The next source of energy is the glycogen - lactic acid system. Glycogen is made up of a bunch of glucose subunits and is broken down into glucose. The first half of this is anaerobic (no oxygen needed) and produces ATP and pyruvic acid. Pyruvic acid can either go through the Krebs Cycle (needs oxygen) or the lactic acid cycle (doesn't need oxygen). If you've ever felt a burning sensation at the end of a long set (which I'm sure you have), that's lactic acid entering your muscles. If I remember correctly, the energy from lactic acid production will give you about 1 or 2 minutes of muscle contractions.

Last, is the aerobic cycle (a.k.a. Krebs cycle and Citric Acid Cycle). This is where the pyruvic acid listed above goes in the presence of oxygen (aerobic activity). It produces ATP much more efficiently, but more slowly, so it's not fast enough for a bench press movement. It will continue to function until you run out of stored fuel in your body.

When you lift weights, you only use the phosphagen system and a very small percentage of the glycogen - lactic acid system. The ATP stored in your muscles I believe all comes from the Krebs Cycle which is slow but very, very efficient. So the phosphagen system (what you use mainly when you lift weights) uses less glucose because of its super-efficient source. Also, phoshocreatine gives off almost twice as much energy as ATP, which adds to its efficiency.

Playing a soccer game, for instance, would use more of the glycogen - lactic acid system. Jogging (or any other aerobic activity that doesn't require any kind of powerful movement) uses the aerobic (oxidative) system.

Sorry so long - you said you wanted a scientific answer and I'm a medical student.

Don't worry, I'm also in medical biology, but it's just that I have that damn biochem course.

I appreciate your answer, that's what I was looking for.

And I just read that we burn less glucose in anaerobic conditions because lactic acid can be retransformed into glucose (and then glycogen) and stored (or used as energy) in the muscles.

Well, thank you very much for your answer, as you made me more intelligent (or at least made me have a better understanding !)

A little bit of lactic acid is converted back into pyruvic acid, but most of it is converted back to glucose in the liver (as you said). That gives less of a net loss of glucose, but that process is completed after you've left the weight room. So it doesn't really contribute to your glucose efficiency while lifting weights.

Originally Posted by m_langlois01

Why is the consumption of glucose greater in aerobic conditions?
Why is the consumption of glucose lower in anaerobic conditions?
Thanks!

Do you mean what the cell consumes or what the organism consumes. Nonfaculative organisms can use glucose for energy by fermentation or oxidation. Every glucose molecule will give a net yield of about 36 ATP when oxidation is taken to completion. Fermentation will yield about 2 ATP per glucose and leave a molecule of Lactic Acid. Oxidation is much more efficient, so an anaerobic organism would need to consume more glucose for the same ATP yield, not less.

I noticed that, too, and I figured he meant glucose used doing a bench press(anaerobic) versus glucose used running a long distance (aerobic). When doing a bench press, most of the energy you use is ATP already stored in the muscles, so you don't need to burn very much glucose compared with running a long distance. Oxidation is a slow process and requires oxygen, so it isn't really applicable to the weight room except that it is probably the primary source of ATP already stored in the muscles.

As far as the metabolic processes themselves go, Oxidation (or Krebs or Citric Acid Cycle or whatever you want to call it) is much more efficient than fermentation (or lactic acid cycle). The only reason the body uses fermentation rather than oxidation while lifting weights is because it needs immediate ATP quickly to get those ten reps up, it can't wait on the long process of oxidation to complete.

Maybe I misunderstood his question. If he meant more glucose is used for oxidation than in fermentation, he was clearly wrong to begin with.

Well, back in 1843, Pasteur measured the consumption of glucose by yeasts in anaerobic conditions, and the consumption of glucose by these same cells where there was oxygen.

So, is the consumption of glucose greater or lower in presence of oxygen? (maybe there's a concept that I didn't understand well) And secondly, why is that? (because right now, I'm totally confused!)

Oh wait, I understand now...

The pyruvate enters the mitochondria where it will be the substrate of different enzymes, where the number of ATP will be greater than in anaerobic conditions. So more ATP means that the cell needs less glucose?

Is that it?

So THIS is why I studied psychology.....

Sorry for the delay - I left to run errands.

By the way, this has pretty much completely veered off the course where it would be applicable to bodybuilding. I had no idea you were just asking generally for a class. But here's the answers to your questions as best I can give them:

Let's assume a mole of glucose goes through glycolysis and becomes two pyruvic acids. That produces 6 ATP and doesn't need oxygen. The pyruvic acid is what enters one of two cycles depending on needs and the presence of oxygen - it enters either oxidation or fermentation. Oxidation produces much more ATP per pyruvate than fermentation, so it is more efficient. If you need to produce 100 ATP, it will take much less oxidation than fermentation to do so.

In your last post you asked about the mitochondria. Yes, oxidation occurs in the mitochondria, and yes, it does produce more ATP than anaerobic conditions would produce.

Initially, being a bodybuilding website, I though you were asking about energy sources as they are applied to lifting weights. That is why I said that less glucose is used say, doing a bench press, because the energy source for a bench press is mostly ATP already stored in the muscle. When doing a bench press or a squat or whatever, oxidation does not have enough time to complete the cycle to produce ATP for repetitions.

Got it?

Originally Posted by m_langlois01

Oh wait, I understand now...

The pyruvate enters the mitochondria where it will be the substrate of different enzymes, where the number of ATP will be greater than in anaerobic conditions. So more ATP means that the cell needs less glucose?

Is that it?

OK. One glucose turns into two pyruvate and releases a net of 2 ATP during glycolysis.

If oxygen is present, the pyruvate molecules enter the mitochondrion and the final result after The Krebs Cycle and The Electron Transport Chain is a total net gain of about 36-38* ATP per glucose molecule.

If oxygen is not present, pyruvate molecules from glycolysis do not enter the mitochondrion, and ferment into lactic acid in the cytosol.

Lactic Acid has lots of potential energy, but the process to use it makes it less efficient than oxidation.

Therefore, the aerobic process yields more ATP per glucose.

*If one counts the energy required to shuttle the 2 molecules of NADH that are created during gylcolysis into the mitochodrial matrix then the net total of ATP from oxidation is closer to 36 than 38.

Originally Posted by PirateFromHell

OK. One glucose turns into two pyruvate and releases a net of 2 ATP during glycolysis.

If oxygen is present, the pyruvate molecules enter the mitochondrion and the final result after The Krebs Cycle and The Electron Transport Chain is a total net gain of about 36-38* ATP per glucose molecule.

If oxygen is not present, pyruvate molecules from glycolysis do not enter the mitochondrion, and ferment into lactic acid in the cytosol.

Lactic Acid has lots of potential energy, but the process to use it makes it less efficient than oxidation.

Therefore, the aerobic process yields more ATP per glucose.

*If one counts the energy required to shuttle the 2 molecules of NADH that are created during gylcolysis into the mitochodrial matrix then the net total of ATP from oxidation is closer to 36 than 38.

That's pretty much right. Glycolysis (one glucose to two pyruvate) actually produces 6 ATP, not 2, and the oxidation of the pyruvic acids yields 30 ATP (15 for each pyruvate) for a TOTAL of 36. Oxidation itself only produces 30, the other 6 comes from glycolysis.

Everything else was right.

Maybe what you were thinking about with the 2 ATP was the fact that glycolysis produces 4 ATP and 2 NADH and expends 2 ATP. Each NADH counts as 2 ATP in the cystol because it becomes 2 ATP, so they say glycolysis produces a net of 6 ATP/ATP equivalents, when it really only directly produces 2 ATP.

Same thing with the Krebs cycle (oxidation). It doesn't actually produce 30 ATP, in fact, it doesn't produce any! It actually produces 3 NADH, one FADH2 and one GTP. Each NADH in the mitochondria counts as 3 ATP, each FADH2 counts as 2 ATP, and each GTP counts as 1 ATP, because they all convert to ATP in the mitochondrion.

And if you do that cycle for both pyruvates, you get 30 ATP/ATP equivalents.

For a total of 36.

Ok, I'm done.

Thanks, that's what I was looking for!

By the way, what are you studying in thatguy?

Glycolysis (one glucose to two pyruvate) actually produces 6 ATP, not 2

One glucose uses 2 ATP and yields 4 ATP by substrate-level phosphorylization (net gain of 2 new ATP per glucose).

Each NADH counts as 2 ATP in the cystol because it becomes 2 ATP

This is another way of looking at it and is inline with what I said. Each NADH yields 3 ATP in the ETC, but the two produced in glycolyis cost the cell about 2 ATP to get in the mitochondria, so the net yield for those two NADH is about 2 ATP each.

each GTP counts as 1 ATP

The GDP has to be phosphorylized in the Krebs Cycle to yield the single ATP per pyruvate (from substrate-level phosphorylization), so it shouldn't be counted as equivalent to ATP.

As far as total ATP equivalency goes, it varies depending on who your source of info is. I sold my bio book yesterday, so I have no reference. But, I bought some nice pants with the money.

Originally Posted by m_langlois01

Thanks, that's what I was looking for!

By the way, what are you studying in thatguy?

I start medical school in July. Studied Biology in college.

Originally Posted by PirateFromHell

But, I bought some nice pants with the money.

LOL. I'd say you came out on top with that trade! Are you still a student or did you graduate?

Originally Posted by thatguy

LOL. I'd say you came out on top with that trade! Are you still a student or did you graduate?

I am currently an undergraduate at The University of Texas, and my major is Nutrition and Health. Good luck with med school, Bro.

Originally Posted by thatguy

If you've ever felt a burning sensation at the end of a long set (which I'm sure you have), that's lactic acid entering your muscles.

Actually, this is a misconception. The burn is actually from Hydrogen ions that are released when lactic acid is broken down to lactate.