• Introduction to Polysaccharides

    • Following disaccharides, polysaccharides are formed by the repetition of sugar units.
    • Each disaccharide retains four hydroxyl (–OH) groups and a hemiacetal group, allowing for further sugar linkages.

  • Cellulose vs. Starch

    • Cellulose:

    • Formed by beta-1,4 glycosidic bonds.

    • Not digestible by humans; our enzymes can’t break these bonds.

    • Structure:

      • It has a stable chain of sugar molecules linked by beta-glycosidic bonds.
      • Each sugar molecule is in a six-membered ring causing strong hydrogen bonding between chains.
      • This makes cellulose flexible, strong, and stable.

    • Function:

      • Structural component of plant cell walls (e.g., wood).

    • Starch:

    • Formed primarily by alpha-1,4 glycosidic bonds, making it digestible.

    • Types of Starch:

      • Amylose:
      • Linear chain with only alpha-1,4 links.
      • Forms helices (similar to DNA), relatively stable.
      • Typically constitutes about 20% of starch and can reach molecular weights of 500,000 Daltons.
      • Amylopectin:
      • Branched structure with both alpha-1,4 and alpha-1,6 bonds.
      • Accounts for about 80% of starch.
      • Contains 100,000 + glucose units, branched approximately every 25 glucose units, creating a hierarchical structure.
      • Results in a micelle structure visible under an optical microscope.

  • Cooking and Starch:

    • Cooking alters the granular structure of starch, making it digestible.

  • Glycogen:

    • Primary form of energy storage in animals.
    • Similar to amylopectin but has random branching, making it hyperbranched.
    • Can contain up to 1,000,000 glucose units.
    • Readily converted back into glucose when the body needs energy.

  • Summary of Key Concepts in Carbohydrate Chemistry:

    • Different types of sugars: monosaccharides, disaccharides, polysaccharides.
    • Structural and functional differences between cellulose, starch, and glycogen.
    • Importance of glycosidic bonds (beta vs alpha) in determining digestibility and function.
    • Basic understanding of sugar projections and isomer configurations (D/L forms, anomers).

  • Exam Preparation Tips:

    • Know definitions and structural differences among sugars.
    • Practice converting between Fischer and Haworth projections.
    • Be familiar with the configurations: alpha and beta anomers, and how these impact functionality of sugars.
    • Understand the implications of polysaccharide structure on digestibility and energy storage.