Glycogen

Introduction

A glucose polymer called glycogen is found in the majority of mammalian and non- mammalian cells, in microbes, and even in some plants. It is a significant and rapid source of stored glucose. As a supply of glucose for other tissues, it is mostly kept in the liver of vertebrates. It appears to be primarily employed in the muscle for energy- related functions as the metabolic fuel for glycolysis, which generates glucose 6- phosphate.

As a result, glycogen is essential as a source of overall and cellular energy as well as an energy reserve. The synthesis and breakdown of glycogen are regulated by a large variety of enzymes and hormones. As a result, factors including nutrition, exercise, and stress can significantly impact glycogen storage in the human body.

What is Glycogen?

Glycogen is a plentiful source of energy for both animals and fungi. Glucose has a polysaccharide structure; it will serve as the body's main method of glucose storage. Glycogen is stored and formed in the liver cells and the four hydrated water compartments of the muscles. It represents yet another type of long-term energy storage. The ability of muscle cells to quickly transform muscle glycogen into glucose and liver glycogen to do the same enables the body to use glucose, including the (CNS) central nervous system.

Structure of Glycogen

Glycogen is a long polymer of glucose units combined with alpha acetal linkage. This acetal connection is produced by the union of the carbonyl group with the alcoholic group. Aldehyde is the carbonyl group present in it, indicated by (-CHO), and if a ketonic group is present it is called hemiacetal. If two alkoxy groups are connected to the same carbon atom, it is a member of the acetal group. The glycogen analogue glucose polymer functions as a kind of energy storage in plants. Its structure is the same as that of the more densely compacted and extensively branched starch amylopectin.

Structure of Glycogen

Functions of Glycogen

When it becomes necessary to maintain normal blood sugar levels, liver glycogen functions as a reserve to store glucose produced by the hepatocyte. For utilisation as an energy source during muscle activity, glucose from glycogen stores is still present in skeletal and cardiac muscles. A modest amount of glycogen is present in the astrocytes of the brain. It is created while you sleep and can be moved as you walk. In type II pulmonary cells of the embryonic lung, it plays a specialised function. These cells can generate lung surfactant and begin producing glycogen around week 26 of pregnancy.

Other Tissues

Other than liver and muscle cells, glycogen is also present in lower quantities in other tissues such as the kidney, red blood cells, and white blood cells. The glucose will be kept in the uterus and stored in glycogen to meet the embryo's energy requirements. Following its breakdown, glycogen will either be released into the bloodstream, or it will enter the glycolytic pathway.

Bacteria and Fungi

To deal with the scarce environmental resources, microorganisms like bacteria and fungus have developed some methods for energy storage; in this case, the main source of energy storage is glycogen. Low levels of carbon, sulphur, or phosphorus are just a few of the nutrients that can cause yeast to produce more glycogen. With a restriction on other necessary nutrients, the bacteria produce glycogen in response to the readily accessible carbon energy sources.

Metabolism of Glycogen

The body can release or retain glucose depending on its energy requirements thanks to the tightly controlled mechanism known as glycogen homeostasis. The processes of glycogen synthesis and breakdown are known as glycogenolysis and glucogenesis, respectively.

Glycogenesis or Glycogen Synthesis

The process of the formation of glycogen by adding glucose into their chains is known as glycogenesis. Uridine Triphosphate provides the necessary energy for glycogenesis.

The glucose-1 phosphate facilitates the conversion of glucose-1 phosphate into glucose. The glycogen protein, which is involved in the manufacture of glycogen, catalyses the attachment of UDP glucose. The glycogen synthase then expands after glucose is added via -1,4 glycosidic connections. The glycogen branching enzyme referred to as branching is catalysed by amyloid 1- 4 to 1- 6 trans glucosidase.

Glycogenolysis or Glycogen Breakdown

The process of breakdown of glycogen to glucose- 1 phosphate with help of certain enzymes is known as glycogenolysis. Through the action of the enzyme glycogen phosphorylase, one molecule of glucose will be removed from the non-reducing end of the compound, resulting in glucose-1 phosphate.

The enzyme phosphoglucomutase is necessary for the conversion of glucose- 1 phosphate, which produces glucose- 6 phosphates. The glucose- 1 phosphate's C-6 will get a phosphate group from phosphoglucomutase's active site, where it will bind to serine and then be transferred. And the release of glucose- 6 phosphates will occur.

Glycogen and Diet

The amount of food consumed, and the activities carried out can affect how much glycogen is produced and how the body will operate. Starting a low-carb diet may cause low-level glycogen, which will cause symptoms of mental drowsiness and exhaustion.

Consumption of a low-carb diet will cause a significant loss of weight. This is primarily due to the glycogen, which will be 3 times the weight of glucose and be made up mostly of water. The rapid water loss will result from the quick decrease in glycogen at the start of the diet.

Exercise causes the body to lose most of its glycogen from the muscles, which results in glycogen depletion. A person can practise carbohydrate loading, which involves consuming large amounts of carbohydrates, to increase their ability to store glycogen while exercising.

Conclusion

Glycogen is a storehouse of energy in our body. And it is the polymer of glucose, which helps to maintain sugar levels in the body. Glycogenesis is the process through which glycogen is formed. The breakdown of glycogen is known as glycogenolysis. A low level of glycogen in the body causes various health problems. Hence it is important to maintain a glycogen balance in the diet.

FAQs

1. Glycogen Metabolism - The Medical Biochemistry Page. Retrieved 2022, from https:/Does glycogen have a helical structure?

The more common bond, the alpha-1,4-glycosidic bond, provides glycogen with a helical structure that is good for storing energy.

2. Where is glycogen found?

It is mostly kept in the liver in vertebrates where it serves as a glucose reserve for other tissues.

3. Why is glycogen important?

The body uses glycogen as a major energy reserve. Therefore, it is necessary for all bodily functions.

4. What happens when there is excess glycogen in the body?

The liver enlarges because of the accumulation of too much glycogen, the energy- storing substance derived from carbs, in the liver.

5. Who discovered glycogen?

Claude Bernard discovered glycogen in 1857.

6. Does glycogenesis occur in the liver?

By regulating different routes of glucose metabolism, such as glycogenesis, glycogenolysis, glycolysis, and gluconeogenesis, the liver plays a significant role in the regulation of glucose homeostasis.