Gluconeogenesis is simply the reverse of glycolysis.

Fructose-2,6-bisphosphate is an important allosteric regulator of glycolysis and gluconeogenesis.

Glycogen metabolism can be controlled by different hormones.

The presence of insulin in the bloodstream after a meal has different effects on different cells in the body.

Glycogen metabolism must be tightly controlled in the cells. If both processes happen at the same time, energy would be wasted. Glycogen metabolism is regulated in two ways:

• Allosteric control of regulatory enzymes.

• Hormonal control by covalent modification of regulatory enzymes.  

Typically, products of a pathway allosterically interact with a regulatory enzyme and inhibit them while a building block of a pathway allosterically interacts with a regulatory enzyme and activate them.

What would happen to glycogen phosphorylase and glycogen synthase if there is a high amount of ATP in the cell?

Anna and Beth have decided to run the Great Ocean Road Marathon this year. Since they have never run a marathon before and don’t usually exercise much, they decide to start practicing early on in preparation.  

They go for a run one early morning and for the first 2-3 minutes everything goes well, but Beth suddenly feels intense cramping and pain in her muscles. They both stop and after resting for about 5 minutes Beth starts to feel better and starts running again.

The same thing happens each time they go for a run and Beth decides to visit a doctor. The doctor diagnoses her with McArdle’s disease and recommends she avoid strenuous exercise.

This disease is caused by a deficiency in the glycogen phosphorylase enzyme which is involved in glycogen breakdown.

Which glycogen phosphorylase is affected?

What is the function of glycogen in the body?

Energy production during strenuous exercise can be divided into two stages. 

Let’s look at what is happening in Anna’s muscle cells. 

Stage 1:

For the first 2-3 minutes, Anna’s body uses up the blood glucose to produce energy through glycolysis. After about 3 minutes the body uses up all the blood glucose and Anna’s muscle cells start breaking down her muscle glycogen to glucose to produce energy through anaerobic glycolysis. Remember, anaerobic glycolysis is a faster way to make ATP during strenuous exercise. This leads to an increase in lactate production and a drop in pH.  

Stage 2:

After about 8-10 minutes, energy production shifts to oxidative phosphorylation. The muscles start using pyruvate from glycolysis AND free fatty acids, glucose, and amino acids from the bloodstream to produce more ATP to allow Anna to keep running.

Compared to Anna, what is happening in Beth's muscle cells that lead to her symptoms?

Which one of these enzymes is not involved in glycogen breakdown?

Which organ in the body stores glycogen to be used by other cells and tissues in the body?