Glycogenolysis

Many biochemical processes occur in our human body to control blood sugar levels. The catabolic and anabolic processes together maintain a sugar level in the bloodstream so that every cell in the body can get ample carbohydrates for energy production. One such process is glycogenolysis. This is a well-controlled pathway where enzymes break glycogen, the stored carbohydrate source to form glucose when the blood sugar level drops. In this section, we will learn more about this biochemical process, where it takes place, and what are its functions.

What is Glycogenolysis?

When we eat food, the excess of the blood sugar absorbed from the assimilation of the different food sources is converted into glycogen by different hormones to store it in the muscles and livers. It is done to create a reserve of energy-producing glucose that can be used in emergency cases or when the blood sugar level is falling in an individual. Hence, we can easily conclude that glycogenolysis occurs in the liver and muscles.

This biochemical process is triggered by epinephrine and the hormone glucagon. This hormone is responsible for initiating the transformation of glycogen to glucose. It is a catabolic process where the glucose monomers are removed from the chains of a glycogen molecule. We can also consider it as a step-down process where the number of carbon atoms reduces in the glycogen molecule.

Mechanism of Glycogenolysis

As mentioned earlier, this is a catabolic process where the polymers of glycogen are broken down into smaller units of glucose. It happens in the presence of an enzyme named glycogen phosphorylase. It is a very complex biochemical reaction where bigger units break into smaller units. If we represent this reaction in the form of an equation, it will look like this:

glycogen(n) + Pi ⇌  glycogen(n-1)  +  glucose-1-phosphate

Here, Pi is the inorganic phosphate released by the action of glycogen phosphorylase. It causes a cleavage in the bond of a glycogen molecule leading to the breaking down of a glucose molecule with the inorganic phosphate attached to it. These bonds are then broken one after the other to produce units of glucose and then released into the bloodstream.

The glycogen debranching biochemical enzyme cleaves the polymer of glycogen until only 4 residual units are left in the chain. This enzyme then sends the three remaining glucose units to other branches of another glycogen unit and exposes the branching locations. This is how the last of the glucose units are broken and released in the form of glucose-6-phosphate produced in the glycogenolysis pathway.

Function of Glycogenolysis

You can understand that this process is done to release the stored glycogen in the form of usable glucose units from the liver and muscles to the bloodstream. The glycogenolysis pathway is followed due to the signalling of the neurons or the hormones produced. It generally happens when the body is under stress for a low blood sugar level or an emergency purpose. When a human encounters a threatening situation, the body starts producing adrenaline or epinephrine. This is called fight or flight response. During this response, the stored glycogen is required as the body prepares for an extreme situation and needs a lot of energy to be produced in the muscles.

During this situation, the muscles will need glucose to burn and produce energy. The body prepares the ground by releasing the glycogen and glycogenolysis enzymes start breaking the chains immediately. When the units of glucose-1-phosphate and glucose-6-phosphate are produced, they are used by the muscle cells or myocytes to break down and produce energy at a considerable level. This helps the person to react during an emergency. He will use this boost in energy to fight or flee from the situation. It also occurs when a person is fasting and the blood sugar level drops. The stored glycogen in the liver is converted into glucose and then released into the bloodstream.

During the fight and flight response, glycogen is broken down in the muscles to make them ready for any action. When the blood sugar level reduces, the cells in different parts of our body sends signals that start to provoke the glycogenolysis enzymes to break it down to maintain the level.

How Glycogenolysis is Regulated?

Glycogenolysis means breaking down glycogen into glucose. It is started by the production of hormones and also controlled by the anti-hormones when not needed. Insulin converts excess blood sugar into glycogen and stores it in the liver and muscles. Glucagon provokes the enzymes to break it down to release glucose in the bloodstream or muscles. It is also controlled by adrenaline. Neural signals in the muscles stop or start this process.

Significance of Glycogenolysis

You have understood what glycogenolysis is, the glycogenolysis definition makes it clearer to understand. The breakdown and release of glucose in an emergency or to control the blood sugar level help us to survive any crisis. It is controlled by the release of hormones like insulin, glucagon, and adrenaline.

Difference Between Glycolysis and Glycogenolysis

Glycolysis is the process where a glucose molecule is broken down into ATP, Pyruvate, and NADH. It is a step-down biochemical process occurring in the cytoplasm. It is the first step of respiration where energy is produced for various cellular activities.

In glycogenolysis, glycogen is broken down into smaller glucose units in the liver and muscles. This process occurs when our body needs blood sugar levels to rise or to get ready for a critical situation during a fight-or-flight response (muscle glycogenolysis).