Difference Between Glycogen and Glucose

The key difference between glycogen and glucose is that glycogen is a polysaccharide that stores carbohydrates in animals and fungi while glucose is the most abundant monosaccharide that works as the primary source of energy in cells.

Carbohydrates are organic compounds characterized carbon, hydrogen and oxygen elements. The ratio of hydrogen to oxygen is 2:1in carbohydrates, similar to water. Carbohydrates are very important widespread biological compounds as they are the chief source of energy and the structural constituent of the protoplasm. In general, carbohydrates are white, solid, and soluble in organic liquids except for certain polysaccharides. Monosaccharides are the basic units of carbohydrate molecules and glucose is the most important of these. Glycogen is also a carbohydrate. But it is a polysaccharide formed by the anabolism of glucose molecules into a branched molecule. Both glucose and glycogen are important in the energy production of the body. Glucose is the main fuel for energy production, and glycogen is a type of secondary, long-term energy storage in animals and fungi.

CONTENTS

1. Overview and Key Difference
2. What is Glycogen 
3. What is Glucose
4. Similarities Between Glycogen and Glucose
5. Side by Side Comparison – Glycogen vs Glucose in Tabular Form
6. Summary

What is Glycogen?

Glycogen is a polysaccharide synthesized in the liver from excess amounts of glucose, fructose and galactose, under the influence of various enzymes. Glycogenesis refers to the glycogen formation process occurring in the liver. In addition, glycogen is a secondary reserve material. Therefore, some amounts of glycogen may be further metabolized into fat and stored in the adipose tissues. Glycogen is non-soluble in water since it is a polysaccharide.

Furthermore, glycogen does not work as a readily available energy source. But, at a sudden demand for energy like a sudden run, glycogen breaks down into glucose to produce the excess amounts of energy through a process called glycogenolysis. Due to this, glycogen depletion can occur during continuous high-intensity exercising, causing intense fatigue, hypoglycemia and dizziness.

The conversion of glucose into glycogen and glycogen back into glucose is entirely under the control of hormones. The islets of Langerhans in the pancreas secrete a hormone called insulin. If the glucose content increases from normal levels (70-100 mg per 100ml of blood), insulin induces the uptake of excess glucose by the liver for the production of glycogen. If the glucose content in the blood decreases from the normal levels, the glucagon hormone acts upon the glycogen storage in the liver to release glucose by glycogenolysis. In this way, our body maintains the fluctuation of the blood glucose in a fairly narrow limit.

What is Glucose?

Glucose is a monosaccharide that contains six carbon atoms and an aldehyde group. Therefore, it is a hexose and an aldose. It has four hydroxyl groups. Though it has a linear structure, glucose can be present as a cyclic structure as well. In fact, in a solution, the majority of the molecules are in the cyclic structure. During the formation glucose cyclic structure, the OH group on carbon 5 transforms into an ether linkage in order to close the ring with carbon 1. This forms a six-member ring structure. The ring is also referred to as a hemiacetal ring due to the presence of carbon that has both ether oxygen and an alcohol group. Because of the free aldehyde group, glucose can be reduced, working as reducing sugar. Furthermore, dextrose is a synonym for glucose; glucose is dextrorotatory since it is able to rotate plane-polarized light to the right.

When there is sunlight, plants synthesize glucose from water and carbon dioxide by the process of photosynthesis. This glucose then goes to storing tissues in order to serve as an energy source later. Animals and human obtain glucose from plant sources. Natural consumable glucose occurs in fruit and honey. It is white and sweet in taste. Furthermore, glucose is soluble in water.

In humans, glucose content in the blood remains at a constant level (70-100 mg per100ml of blood). Cellular respiration oxidizes this circulating glucose in order to produce energy in the cells. Homeostasis is the mechanism that regulates blood glucose level in human by insulin and glucagon. Furthermore, a high glucose level in blood leads to a diabetic condition.

What are the Similarities Between Glycogen and Glucose?

• Glycogen and glucose are two forms of carbohydrates.
• They are good energy sources in living organisms.
• Glycogen breaks down into glucose to answer sudden energy demands.
• Both are made up of carbon, hydrogen and oxygen.

What is the Difference Between Glycogen and Glucose?

Both glycogen and glucose are carbohydrates. But, glycogen is a branched polysaccharide while glucose is a monosaccharide. This is the key difference between glycogen and glucose. Furthermore, glycogen is the major carbohydrate storage form in animals, while glucose is the primary energy source in living cells. Another difference between glycogen and glucose is that glycogen is poorly soluble in water while glucose is readily soluble in water. In addition, glucose is found in all living organisms whereas glycogen is found only in animals and fungi. Furthermore, glucose provides energy for regular functions of the body, but glycogen supplies the energy for strenuous exercises including the function of the central nervous system.

Summary – Glycogen vs Glucose

Glucose and glycogen are carbohydrates. Glycogen is the storing form of carbohydrates in animals. On the other hand, glucose is a simple sugar that works as the primary energy source. Moreover, glucose is a monosaccharide while glycogen is a polysaccharide. Glycogen is the storage type of glucose that is formed and kept in the muscles, liver and even in the brain. Glycogen is a secondary energy reserve. In fact, it is a back-up energy source when glucose becomes unavailable. Both these are essential for the health of a well functioning organism. This summarizes the difference between glycogen and glucose.

Reference:

1.“Glycogen.” Glycogen – an Overview | ScienceDirect Topics, Available here.
2. “Glucose.” Wikipedia, Wikimedia Foundation, 2 Sept. 2019, Available here.

Image Courtesy:

1. “Glycogen structure” By Mikael Häggström (CC0) via Commons Wikimedia
2. “DL-Glucose” By NEUROtiker – Own work (Public Domain) via Commons Wikimedia