Glycogen vs Glucose
Carbohydrates are compounds normally characterized by having carbon, hydrogen and oxygen elements in their molecules in which the ratio of hydrogen and oxygen is the same as in water (2:1). 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. The basic units of the carbohydrate molecules are known as monosaccharide, 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 associated with the energy production of the body. Glucose is the foremost fuel for energy production, and glycogen is a type of secondary, long- term energy storage in animals and fungi.
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 and has the following structure.
Though it is shown as a linear structure, glucose can be present as a cyclic structure too. In fact, in a solution, majority of the molecules are in the cyclic structure. When a cyclic structure is forming, the -OH on carbon 5 is converted into the ether linkage, to close the ring with carbon 1. This forms a six member ring structure. The ring is also called a hemiacetal ring, due to the presence of carbon that has both an ether oxygen and an alcohol group. Because of the free aldehyde group, glucose can be reduced. Thus, it is called a reducing sugar. Further, glucose is also known as dextrose because, it rotates plane polarized light to the right.
When there is sunlight, in plant chloroplasts, glucose is synthesized using water and carbon dioxide. This glucose is stored and used as a source for energy. Animals and human obtain glucose from plant sources. Natural consumable glucose occurs in fruit and honey. It is white, sweet in taste, and soluble in water. The complex carbohydrates contained in the food are subjected to the action of the enzymes present in saliva, pancreas and intestinal juices, and are converted into monosaccharides. The starch components are hydrolyzed to glucose in the intestine itself. The other types of carbohydrates are converted to galactose and fructose, which are later converted to glucose in the liver. Glucose is then passed into the blood.
The glucose content in the blood remains at a constant level (70-100 mg per100ml of blood). This circulating glucose with the oxygen produces energy in the cell through the process of cellular respiration. Glucose level in human blood is regulated by homeostasis mechanism. Insulin and glucagon hormones are involved in the mechanism. When there is high glucose level in blood, it is called a diabetic condition. The measurement of blood sugar level measures the glucose level in blood. There are various means to measure the blood glucose level.
The synthesis of glycogen occurs in the liver. The excess amounts of glucose, fructose and galactose, under the influence of various enzymes, are converted into glycogen through a process called glycogenesis. It is a secondary reserve material. The produced glycogen may be further metabolized into fat and stored in the adipose tissues. Glycogen is non-soluble in water. At a particular sudden demand of energy like a sudden run, glycogen is converted to glucose to produce the excess amounts of energy through the process of glycogenolysis. Glycogen depletion can occur during continuous high intensity exercising, causing intense fatigue, hypoglycemia and dizziness.
The conversion of glucose in to glycogen and glycogen back in to glucose is entirely under the control of hormones. The islets of Langerhan 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 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, the fluctuation of the blood glucose is kept in a fairly narrow limit.
What is the difference between Glycogen and Glucose?
• Glucose is essentially a monosaccharide soluble in water and sweet in taste. Glycogen is a branched polysaccharide, which is insoluble in water and is not a sugar. However, it gives a blue colour when subjected to a KI/I2 solution, but glucose does not.
• Glucose is found in all living organisms where as glycogen is found in only animals and fungi.
• Glucose is a primary source of energy, but glycogen is a secondary energy reserve.
• The glucose level in the blood is subjected to hormonal regulation, but glycogen is regulated as a secondary effect of that process.
• 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.
• Both these are essential for the health of a well functioning organism.