Glycogen is a branchedpolysaccharide(also called a polycarbohydrate) composed of many glucose molecules linked together.
This article will explore what glycogen is and the important roles it has in the body.
It will also discuss how to maintain glycogen levels.
SCIEPRO/SCIENCE PHOTO LIBRARY / Getty Images
SCIEPRO/SCIENCE PHOTO LIBRARY / Getty Images
Glycogen Structure
Glycogen is a highly branched glucose polymer.
A polymer is a substance that consists of very large molecules.
Most of the glucose units are linked linearly by the alpha-1,4-glycosidic bonds.
Branch points occur at roughly every eight to 10 glucose units via alpha-1,6 glycosidic linkage.
A fully formed glycogen molecule is believed to contain around 55,000 glucose units.
Every glycogen molecule also has glycogenin, a protein involved in glycogen synthesis.
Excess glucose gets stored short term in the liver and muscles as glycogen or long term as fat.
Liver glycogen acts as a reservoir for your body’s glucose to help maintain normal blood glucose levels.
When we need additional energy, enzymes break down glycogen to supply the body with glucose.
Glucose broken down from liver glycogen is the body’s main source of energy.
However, its functions in these areas are largely unknown.
How Much Glycogen Do I Have?
Glycogen Metabolism
The two main metabolic pathways of glycogen are glycogenesis and glycogenolysis.
In short, glycogenesis is the formation of glycogen from glucose molecules.
Glycogenolysis, on the other hand, is the breakdown of glycogen into glucose molecules.
Glycogenesis
Glycogenesis is the process of forming glycogen from glucose.
Glycogen is produced depending on the body’s demand for energy and glucose.
The synthesis of glycogen requires energy from the high-energy nucleotide uridine triphosphate (UTP).
The first step of glycogenesis is the conversion of glucose into glucose-6-Phosphate.
This reaction is catalyzed by the enzyme hexokinases.
Glucose-1-phosphate then reacts with UTP to form UDP (uridine diphosphate)-glucose.
This reaction is catalyzed by UDP-glucose pyrophosphorylase.
Glycogen is first synthesized by the protein glycogenin, which acts as a primer to initiate glycogen synthesis.
Next, the enzyme glycogen synthase extends the chain by adding glucose through alpha-1,4 glycosidic linkages.
It primarily takes place in liver and muscle cells.
Next, glucose-1-phosphate is converted to glucose-6-phosphate by the enzyme phosphoglucomutase.
From there, glucose-1-phosphate can enter the glycolytic pathway.
If glucose-6-phosphatase is present, free glucose can be formed and released into the bloodstream.
This process can happen in the liver but not in the muscle in which glucose-6-phosphatase is absent.
Glycogen and Exercise
Glycogen stores in the muscle and liver decline during physical activity.
As a result, a person may experience fatigue, weakness, and decreased performance.
When glycogen stores become depleted, your body will begin to metabolize fat for energy.
It is often because of a genetic enzyme defect passed down to children from their parents.
However, some forms can also appear later in life.
Several different enzymes are utilized by the body to store glycogen.
As such, there are many different types of GSD.
It is mainly synthesized in the liver and muscle cells.
Glycogen is a readily available form of glucose and can provide rapid energy when needed.
It also plays a role in maintaining our blood glucose concentration.
Physical activity can lower glycogen stores resulting in fatigue and decreased performance.
The best way to maintain glycogen levels in the body is by consuming enough carbohydrates.
A Word From Verywell
Glycogen plays an important role in keeping your body fueled.
Glycogen levels vary depending on your diet, body mass, and exercise frequency.
If you find yourself exhausted during a high-intensity workout or endurance training, your glycogen levels may be depleted.
Frequently Asked Questions
Glycogen is a polymer made up of glucose molecules linked together by glycosidic bonds.
Glycogen plays a key role in keeping our muscles fueled during exercise.
It also helps maintain healthy blood sugar levels.
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