Glycogenolysis: Definition & Pathway

Instructor: Laura Foist

Laura has a Masters of Science in Food Science and Human Nutrition and has taught college Science.

In this lesson we will learn about glycogenolysis and how it provides glucose for energy in the body. We will learn how the glucose is stored and how glycogenolysis get the glucose out of storage form and into the body.

Glycogenolysis Definition

Think about a time that you ran a sprint or raced your friend to the kitchen to get the last piece of pie. Both of these times you needed energy fast. And while you didn't need the energy for long, you did need quite a bit of energy. The fastest source of energy that our body has is in the form of glucose, which is just a simple sugar that our body uses for energy. We find glucose in carbohydrates that we eat. In order to have a reservoir of quick energy, our body will store up glucose.

The storage form of glucose in the human body is glycogen. Glycogen is primarily stored in the liver. Glucose needs to be stored for a quick source of energy when the body needs it. If we didn't have a storage of glucose then when we needed to react quickly we wouldn't be able to. Glucose is also the only source of energy that the brain can use. Without glucose our brain would shut down. This is the structure of glycogen:

Structure of glycogen

Each link and each branch represents an individual glucose molecule that can be used for energy. The process to break the glycogen down into individual glucose molecules is called glycogenolysis. Lysis means 'to break down'. So the name literally means 'to break down glycogen'.

Glycogenolysis Pathway

So when you were racing your friend to grab the last piece of pie, you probably hadn't recently eaten many carbohydrates (unless you already took the second to last piece, and in that case you should probably just let your friend have the last piece of pie). So where did you get that fast burst of energy to sprint to your pie? When you had eaten earlier, you more than likely had some carbohydrates in that meal. Yet you couldn't use all of those immediately. So instead your body saved some of that energy in the form of glycogen.

As soon as your body needed energy, it was able to quickly take glucose from your blood to use for energy and then replace that blood glucose. It is able to do this quickly because the process of breaking glycogen down into glucose is fairly simple for the body to perform. As the glycogen gets broken down, the glucose obtained is used to replace the glucose in the blood.

Look at this picture of glycogen again:

Structure of glycogen

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