Question

What is the advantage of storing glucose as glycogen in animals instead of as monomeric glucose?
(a) Energy obtained from glycogen is more than that from corresponding glucose
(b) Glucose present as monomers within the cell exerts more osmotic pressure than a single glycogen molecule, resulting in loss of water from the cells
(c) Glucose present as monomers within the cell exerts more osmotic pressure than a single glycogen molecule, resulting in excess water within the cell
(d) Glycogen gives more rigidity to the cell

Answer 1

Hint: Glycogen is a highly branched polysaccharide of glucose. Due to its bulky nature, glycogen cannot dissolve in the medium of the cell. This property is in contrast with the glucose which can easily dissolve in the cellular medium and thus change a cell’s environment.

Complete answer:
The monomers ‘glucose’ are linked to each other via ɑ-1,4-glycosidic linkages. Branches arise by ɑ-1,6-glycosidic bonds at about every 10th residue. In the cell, they exist as granules along with enzymes catalyzing its synthesis and usage. In animal cells, glucose is generally stored in the form of glycogen. This is done to not upset the osmotic balances in the cell. Glucose molecules are soluble in water and thus can cause the cell to become hypertonic. This will result in the entry of water molecules within the cells and cause it to lyse. On the other hand, glycogen is insoluble in water and therefore stays inert. It does not cause any imbalance in osmotic pressure. But glucose monomers, when compared to glycogen in the cell, exerts more osmotic pressure resulting in excess water within the cell.

Additional Information: -The major sites for storage of glycogen in animals are muscle and liver. Although its concentration is higher in the liver, the much greater mass of skeletal muscles stores a greater total amount of glycogen. -The liver can mobilise its glycogen to fulfil the need for glucose in any part of the body, but muscle can only use its glycogen to satisfy its own energy needs.
-Glycogen is synthesised from glucose-6-phosphate in the process of glycogenesis. This is favoured by insulin, a polypeptide hormone secreted by the pancreas. It aims to reduce the blood glucose concentration and thus stimulates its conversion to glycogen.
So, the correct answer is ‘Glucose present as monomers within the cell exerts more osmotic pressure than a single glycogen molecule, resulting in excess water within the cell.’

Note: -Many diseases have been characterised with the deficiency of enzymes for glycogen metabolism and thus impairs its storage.
-Hers’ disease is a glycogen storage disease which results due to the deficiency of phosphorylase in the liver. This enzyme breakdowns glycogen into glucose when required. Upon its deficiency, the buildup of glycogen in the liver causes hepatomegaly or its enlargement.