Lecture Notes: Disaccharides in Carbohydrates

Introduction to Disaccharides

• Disaccharides are carbohydrates made up of two monosaccharides.
• Linked via condensation reaction, forming a glycosidic bond (a type of covalent bond).

Key Concepts

1. Condensation Reaction

   • Process of linking two monosaccharides by removing a water molecule (H2O).
   • Forms a covalent bond, specifically a glycosidic bond.

2. Glycosidic Bond

   • A type of covalent bond found only in carbohydrates.
   • Different from other covalent bonds in proteins, lipids, or nucleic acids.

Revision: Monosaccharides

• Types of monosaccharides: triose, pentose, hexose.
• Focus on hexose sugars: alpha-glucose, beta-glucose, fructose, galactose.
• Today's focus is on alpha-glucose and fructose.

Examples of Disaccharides

1. Maltose

   • Made of two alpha-glucose molecules linked by a glycosidic bond.
   • Requires specific alpha 1-4 glycosidic bonds.
   • Incorrect: Two alpha-glucose molecules not linked are not maltose.

2. Sucrose

   • Composed of one alpha-glucose and one fructose molecule.
   • Known as table sugar.
   • Linked by glycosidic bonds.

Formation of Disaccharides

• Maltose Formation

  • Two alpha-glucose undergo condensation.
  • Remove one H2O molecule to form a glycosidic bond.
  • Focus on carbon 1 and carbon 4 for the bond (alpha 1-4).

• Sucrose Formation

  • Alpha-glucose linked to fructose.
  • Recognize structure without drawing.

Molecular Formulas

• Maltose: C12H22O11 (not C12H24O12).
• Sucrose: C12H22O11 (same error prevention as maltose).

Hydrolysis

• Opposite of condensation.
• Breaks down disaccharides into monosaccharides using water.
• Example: Breaking maltose into two alpha-glucose.
• Processes involve adding water to break the glycosidic bond.
• Involves hydrolysis (lysis = break, hydro = water).

Important Points

• Disaccharides are specific in their formation and bonds.
• Different glycosidic bonds form different molecules, e.g., alpha 1-4 forms maltose.
• Not all glycosidic bonds are common; alpha 1-4 and alpha 1-6 are most common.
• Hydrolysis is essential to revert disaccharides into original monosaccharides.