What are the structure and functions of cellulose and starch in plants and glycogen in humans?

SouravNovember 8, 2024

Answer

Cellulose, starch, and glycogen are polysaccharides that serve crucial roles in plants and humans. They differ in structure, function, and the organisms in which they are found. Here’s a detailed overview:

Cellulose

Structure

• Composition: Cellulose is composed of long, unbranched chains of glucose molecules linked by β-1,4-glycosidic bonds. This linkage causes every other glucose unit to be inverted, resulting in a linear configuration.
• Microfibrils: The cellulose chains aggregate to form microfibrils through hydrogen bonding, creating a rigid structure that provides tensile strength to plant cell walls. These microfibrils are further embedded in a matrix of hemicellulose and pectin, contributing to the overall strength and integrity of the cell wall.

Functions

• Structural Support: Cellulose is the primary component of plant cell walls, providing rigidity and structural support. This is essential for maintaining plant shape and resisting external pressures.
• Water Regulation: The structure of cellulose helps plants manage water retention and withstand osmotic pressure.
• Digestive Health: Although humans cannot digest cellulose due to the lack of necessary enzymes, it plays an important role as dietary fiber, aiding in digestion and promoting gut health.

Starch

Structure

• Composition: Starch is a polymer made up of glucose monomers linked primarily by α-1,4-glycosidic bonds, with branching occurring via α-1,6-glycosidic bonds. It exists mainly in two forms:
  • Amylose: A linear chain of glucose units (about 20-30% of starch), which tends to form a helical structure.
  • Amylopectin: A highly branched structure (about 70-80% of starch), which allows for more compact storage.

Functions

• Energy Storage: Starch serves as the main energy storage molecule in plants. It is synthesized during photosynthesis and stored in organs such as roots, tubers, and seeds.
• Energy Release: When energy is needed, starch can be enzymatically broken down into glucose monomers for use in cellular respiration.

Glycogen

Structure

• Composition: Glycogen is similar to amylopectin but is more extensively branched. It consists of glucose units linked by both α-1,4-glycosidic bonds (for linear chains) and α-1,6-glycosidic bonds (for branching). This highly branched structure allows for rapid mobilization of glucose.

Functions

• Energy Storage: Glycogen acts as the primary energy storage form in animals and fungi. It is predominantly stored in the liver and skeletal muscles.
• Quick Energy Release: Glycogen can be rapidly converted back into glucose when energy is required, particularly during periods of intense physical activity or fasting. In the liver, glycogen helps maintain blood glucose levels.

Summary Table