Occurrence, Structure and Functions of homoglycans-Starch, Glycogen, Cellulose, Dextrin, Inulin and Chitins.

Homoglycans, also known as homopolysaccharides, are polysaccharides that consist of only one type of monosaccharide unit. Here's an overview of the occurrence, structure, and functions of some common homoglycans: starch, glycogen, cellulose, dextrin, inulin, and chitins.

Starch

Occurrence:

  • Found primarily in plants, especially in seeds, tubers, and roots.

Structure:

  • Composed of two types of glucose polymers: amylose and amylopectin.
    • Amylose: Linear or slightly branched chains of α-D-glucose units linked by α(1→4) glycosidic bonds.
    • Amylopectin: Highly branched chains with α(1→4) glycosidic bonds in the linear segments and α(1→6) glycosidic bonds at the branch points.

Functions:

  • Serves as the primary energy storage carbohydrate in plants.
  • Provides energy for growth and metabolic activities.

Glycogen

Occurrence:

  • Found in animals, particularly in liver and muscle tissues.

Structure:

  • Similar to amylopectin but more highly branched.
  • Composed of α-D-glucose units with α(1→4) glycosidic bonds in the linear segments and α(1→6) glycosidic bonds at the branch points.

Functions:

  • Serves as the main storage form of glucose in animals.
  • Provides a readily available source of energy during periods of high demand.

Cellulose

Occurrence:

  • Found in the cell walls of plants, algae, and some bacteria.

Structure:

  • Linear chains of β-D-glucose units linked by β(1→4) glycosidic bonds.
  • Chains are held together by hydrogen bonds, forming microfibrils.

Functions:

  • Provides structural support to plant cells.
  • Contributes to the rigidity and strength of plant tissues.

Dextrin

Occurrence:

  • Formed as intermediate products during the hydrolysis of starch.

Structure:

  • Composed of short chains of α-D-glucose units linked by α(1→4) glycosidic bonds.
  • Can vary in chain length and branching.

Functions:

  • Used as a thickening agent in food and pharmaceuticals.
  • Serves as a carbohydrate source in some industrial processes.

Inulin

Occurrence:

  • Found in certain plants, particularly in the roots and tubers (e.g., chicory, Jerusalem artichoke).

Structure:

  • Composed of fructose units linked by β(2→1) glycosidic bonds, typically terminating with a glucose unit.
  • Forms a linear or slightly branched structure.

Functions:

  • Serves as a storage carbohydrate in some plants.
  • Acts as a dietary fiber and prebiotic in human nutrition, promoting the growth of beneficial gut bacteria.

Chitins

Occurrence:

  • Found in the exoskeletons of arthropods (e.g., insects, crustaceans) and the cell walls of fungi.

Structure:

  • Composed of N-acetyl-D-glucosamine units linked by β(1→4) glycosidic bonds.
  • Forms long, linear chains that can interact to form strong fibers.

Functions:

  • Provides structural support and protection in arthropods and fungi.
  • Used in various industrial applications, including biodegradable films and medical materials.

These homoglycans play crucial roles in the biological systems where they occur, serving functions ranging from energy storage to providing structural integrity.












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