Glycolysis + Glycogen

[Chemhalp]

Explain the difference in atp yield when glycogen rather than glucose is used as the starting point glycolysis
In outlining the process of glycolysis explain the difference in atp yield when glycogen rather than glucose is used as the starting point :

Please give me a full essay answer, or notations for an essay answer.

I've been looking everywhere and my textbook doesn't show when glycolysis starts with glycogen.

My first thoughts drifted to the difference in ATP yield between anerobic respiration and aerobic.

Any pointers will be great

[MisterATP]

I am not surprise that you haven't found a glycogen as a starting point because liver does good job by making free glucose (from glucose-1-phosphate (product of glycogen degradation)) which is used by all body cells. So actually, glycogen as a starting point of glycolysis is just in cells whose store it. That are cells of liver, kidney and muscles (latter store glycogen for its own needs). As I remember, no ATP is required to remove glucose from glycogen stores.
SO the yield of ATP doesn't change.

[Chemhalp]

So if the body was hypoglycemic, the glycogen can be converted back to G6P and then converted to Glucose anyway?

Stupid essay question trying to trick me

[Wingnut]

I'm not inclined to do homework, but I'll help you out with a hint or two.

In fact, there is a difference in ATP yield when metabolizing glycogen. Here is the hint: the first enzyme involved is glycogen phosphorylase. Once you have researched that, you should have your answer... after the step catalyzed by glycogen phosphorylase, there is a second enzyme involved (I'll let you find that on one your own) and then the resulting moiety enters glycolysis... and it's going to be up to you to figure out at which step, but it shouldn't be too hard.

With the above information, you should be able to calculate the net yield of ATP per glucose unit.

Now, if you REALLY want to wow your instructor, include a paragraph that considers the energetics of producing glycogen in the first place, which I bet you already know, and see if the overall process of glucose-->glycogen-->-->-->pyruvate has any net change in ATP production, and if it is negative or positive compared to simply metabolizing the glucose via glycolysis...

[MisterATP]

Ok, You noted two enzymes. If there is difference in ATP yield, which one requires ATP for catalization of a reaction?

[Wingnut]

Well, like I said, I don't want to do someone's homework for them. There is enough information there to seek out the answer...

[MisterATP]

Never mind whom we help by discussing. I just want to learn for myself and find out how it is really.Ok?

[Wingnut]

Well, glycogen phosphorylase catalyzes the cleavage of a glucose from glycogen by inorganic phosphate, resulting in the formation of glucose-1-phosphate WITHOUT needing an ATP... does that help?

[MisterATP]

Yes, I know it and I totally agree with you. So do you want to say that second enzyme forms glucose-6-phosphate from glucose-1-phosphate WITH needing ATP?

[Wingnut]

No, phosphoglucomutase does not require ATP...

That;s the whole point. By metabolizing glycogen, you produce glucose-6-P without hydrolyzing an ATP... that increases your net yield of ATP...

[juliana29]

Glycogen is a polymer of glocose that is linked together by bonds. ATP energy is made available to muscle by metabolizing muscle glycogen into pyruvate through glycolysis.

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juliana