Disaccharides and polysaccharides

Overview of Disaccharides

  • Definition: Disaccharides are formed from two monosaccharides through condensation reactions.

  • Examples: Maltose, sucrose, lactose.

Structure and Formation

  • Formation: Two monosaccharides link via a glycosidic bond in a condensation reaction, producing water.

  • Hydrolysis Reaction: Disaccharides break down into monosaccharides when water is added.

  • Types of Glycosidic Bonds:

    • 1-4 Glycosidic Bond (e.g., in maltose and lactose)

    • 1-2 Glycosidic Bond (e.g., in sucrose)

Types of Disaccharides

  • Maltose:

    • Made of glucose + glucose, linked by a 1-4 glycosidic bond. A reducing sugar.

  • Sucrose:

    • Made of glucose + fructose, linked by a 1-2 glycosidic bond. A non-reducing sugar.

  • Lactose:

    • Made of glucose + galactose, linked by a 1-4 glycosidic bond. Galactose is a reducing sugar.

Function of Disaccharides

  • Provide a quick release source of ATP.

  • Easily converted to monosaccharides for absorption in the bloodstream.

  • High solubility due to hydroxyl groups, forming hydrogen bonds with water.

  • Sweet taste like monosaccharides.

Polysaccharides

  • Definition: Polymers made of many monosaccharides linked by glycosidic bonds.

  • Storage and Structure: Polysaccharides are compact, chemically inactive, and insoluble in water.

  • Examples: Starch (amylose and amylopectin), glycogen, cellulose.

Starch

  • Amylose: Unbranched, coiled structure with 1-4 glycosidic bonds, compact for storage.

  • Amylopectin: Branched structure with both 1-4 and 1-6 glycosidic bonds, allowing quick hydrolysis.

Glycogen

  • Similar to amylopectin but has more branching, allowing rapid glucose release during cellular respiration.

Cellulose

  • Composed of beta-glucose, forms straight chains allowing hydrogen bonding that provides structural strength in plant cell walls.

  • Arranged into microfibrils for enhanced strength.

Key Reactions

  • Condensation: Links monosaccharides with the loss of water.

  • Hydrolysis: Breaks disaccharides into monosaccharides with the addition of water.

Summary of Key Points

  • Understanding disaccharides’ structure, formation, and function is critical for studies on carbohydrates.

  • The relationship between structure and function in polysaccharides affects their roles in energy storage and structural functions in cells.