10.1.4. Polysaccharides

Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages. These are the most commonly encountered carbohydrates in nature. They mainly act as the food storage or structural materials.

Polysaccharides are complex carbohydrates made up of many monosaccharide units linked together through glycosidic bonds. These connections allow the formation of large molecules that serve essential functions in living organisms, such as energy storage and providing structure. For example, starch and cellulose are two common types of polysaccharides, found in plants, serving different roles in nature.

Think of polysaccharides like long chains of beads (monosaccharides) strung together. Just as a necklace can be used for decoration, the long chains of sugars help in storing energy (like starch in potatoes) or providing structure (like cellulose in plant cell walls).

Starch is the main storage polysaccharide of plants. It is the most important dietary source for human beings. High content of starch is found in cereals, roots, tubers and some vegetables. It is a polymer of a-glucose and consists of two components—Amylose and Amylopectin.

Starch serves as the primary storage form of energy in plants. It is composed of two types of molecules: amylose and amylopectin. Amylose, constituting about 15-20% of starch, is a long, unbranched chain of glucose molecules. Amylopectin, making up about 80-85% of starch, is more complex and branched. Both these components enable plants to store glucose, which can later be broken down and used as energy when needed.

Consider starch like a pantry stocked with sugar (energy). Just like a pantry can have both boxes of cereal (amylose) and jars with different ingredients (amylopectin), plants use starch to ensure they have enough energy stored for when they need it. When you eat foods like bread or potatoes, you are consuming starch for energy.

Amylose is water soluble component which constitutes about 15-20% of starch. Chemically amylose is a long unbranched chain with 200-1000 a-D-(+)-glucose units held together by C1– C4 glycosidic linkage. Amylopectin is insoluble in water and constitutes about 80-85% of starch.

Amylose has a straight chain structure held together by specific glycosidic bonds, making it soluble in water. In contrast, amylopectin has a branched structure which makes it less soluble. These differing structures affect how the body processes these components: amylose releases glucose more slowly than amylopectin, providing a more sustained energy release.

Imagine amylose as a straight, easy-to-unroll tape versus amylopectin as a tangled ball of string that has branches. The straight tape (amylose) can unroll quickly and easily, while the tangled ball (amylopectin) takes longer to unravel but offers different benefits in fixing energy storage.

Cellulose occurs exclusively in plants and it is the most abundant organic substance in plant kingdom. It is a predominant constituent of cell wall of plant cells.

Cellulose is a type of polysaccharide that forms the structure of plant cell walls. Unlike starch, cellulose consists of β-D-glucose units linked together differently, making it rigid and strong. This strength helps plants maintain their shape and provides structural integrity, allowing them to stand tall and resist environmental pressures.

Think of cellulose like the frame of a house. Just like a strong frame supports the house's shape and helps it withstand winds or rains, cellulose provides the necessary support for plant cells. Without cellulose, plants would collapse under their own weight!

The carbohydrates are stored in animal body as glycogen. It is also known as animal starch because its structure is similar to amylopectin and is rather more highly branched.

Glycogen serves as the major energy storage polysaccharide in animals, resembling starch in plants. Glycogen has a highly branched structure, allowing for quick release of glucose when the body requires energy. This branching is crucial for maintaining blood glucose levels during periods without food intake.

Glycogen can be compared to a well-connected network of highways. Just like multiple routes allow cars (glucose) to exit quickly from a highway (glycogen) to reach their destinations (body's energy needs), glycogen’s branched structure enables rapid access to energy.

--