Biomacromolecules, also known as biological macromolecules, are large, complex molecules that play crucial roles in various biological processes and are essential for life. These molecules are the building blocks of living organisms and are responsible for their structure, function, and regulation. Biomacromolecules are typically composed of smaller units called monomers, which are linked together to form larger polymers. There are four main classes of biomacromolecules: Proteins, Lipids, Carbohydrates, and Nucleic Acid.


Carbohydrates: The Fundamental Biomolecules


  • Carbohydrates are one of the primary classes of biomolecules, along with proteins, nucleic acids, and lipids. They are organic compounds composed of carbon (C), hydrogen (H), and oxygen (O) atoms. The term "carbohydrate" means "hydrates of carbon," indicating the presence of hydrogen and oxygen in a 2:1 ratio, similar to water.


  • Monosaccharides are the building blocks of carbohydrates. These are simple sugars with the general formula (CH2O)n, where "n" can range from 3 to 7 or more. Common monosaccharides include glucose, fructose, and ribose.

Types of Carbohydrates:

  1. Monosaccharides:

    • Single sugar units.
    • E.g., Glucose is the primary energy source for many organisms.
    • Other examples include fructose, galactose, and ribose.
  2. Disaccharides:

    • Formed by the condensation (dehydration) of two monosaccharides.
    • E.g., Sucrose (glucose + fructose) and lactose (glucose + galactose).
  3. Oligosaccharides:

    • Short chains of monosaccharides (3-10 sugar units).
    • Often found in cell recognition and signaling.
  4. Polysaccharides: Complex Carbohydrates


    • Polysaccharides are large and complex carbohydrates made up of many monosaccharide units (simple sugars) linked together through glycosidic bonds. Polysaccharides can be linear or branched, and they can be made up of the same type of monosaccharide (homopolysaccharide) or different types of monosaccharides (heteropolysaccharide).

Types of Polysaccharides:

  1. Starch:

    • Source: Found in plants, especially in storage organs like seeds and tubers.
    • Structure: Composed of amylose (a linear chain of glucose) and amylopectin (branched chains of glucose). They form a helical secondary structure and can hold I2  molecules in this helical portion.
    • The Starch-I2  is blue in colour.
    • Function: Starch serves as a primary energy storage polysaccharide in plants.
    • Digestibility: Digestible by enzymes like amylase to yield glucose, providing energy.
  1. Glycogen:

    • Source: Present in animals, particularly in the liver and muscles.
    • Structure: Highly branched structure of glucose units.
    • Function: Glycogen functions as the primary energy storage polysaccharide in animals.
    • Digestibility: Readily broken down into glucose during metabolic processes for energy production.


  1. Cellulose:

    • Source: Found in the cell walls of plants.
    • Structure: Long, linear chains of glucose connected by β-1,4-glycosidic bonds. They do not have complex helices and hence cannot hold I2.
    • Function: Provides structural support to plant cell walls, imparting rigidity.
    • Digestibility: Not digestible by most animals due to lack of cellulase enzymes; serves as dietary fiber, aiding in digestion.


  1. Chitin:

    • Source: Present in the exoskeletons of arthropods (e.g., insects, crustaceans) and cell walls of fungi.
    • Structure: Similar to cellulose, but with N-acetylglucosamine units.
    • Function: Provides structural support and protection to the exoskeletons of various organisms.
    • Digestibility: Not digestible by humans; acts as a source of dietary fiber.

Functions of Polysaccharides

Polysaccharides have a variety of important functions in organisms, including:

  • Energy storage: Polysaccharides, such as starch and glycogen, are used to store energy in plants and animals.
  • Structural support: Polysaccharides, such as cellulose and chitin, provide structural support to plants and fungi.
  • Cell recognition and adhesion: Polysaccharides, such as hyaluronic acid and chondroitin sulfate, play important roles in cell recognition and adhesion.
  • Lubrication: Polysaccharides, such as hyaluronic acid and synovial fluid, lubricate joints and other tissues.