Carbohydrates and Disaccharides

Carbohydrate Overview

• Focus on disaccharides formed from monosaccharides.
• Disaccharides consist of two monosaccharides linked together.

Tyndall Effect Experiment

• Tyndall Effect: Light beam passes through the dissolved substance; no scattering indicates small structures.
• Disaccharides (and monosaccharides) do not scatter light, forming transparent solutions, indicating they are small molecules.

Formation of Disaccharides

• Dehydration Condensation: Combines two monosaccharides by releasing water.
  • Condensation: The joining of two molecules.
  • Dehydration: Loss of water in the process.
• Reaction overview: 2 monosaccharides → Disaccharide + Water.
  • The necessary water molecules are derived from hydroxyl groups on monosaccharides.

Monosaccharides as Building Blocks

• Common monosaccharides include D-glucose, D-fructose, and D-galactose (all hexoses with six carbon atoms).
• Hydroxyl groups on these sugars facilitate linkage during condensation.

Describing Disaccharides

1. List the two monosaccharides: e.g., lactose made from beta D-galactose and beta D-glucose.
2. Identify the carbons involved in forming water: Carbon positions determine hydroxyl contributions to water formation.
   • Hydroxyls at specific carbon positions (C1, C2, etc.) are crucial for linkage.
3. Specify anomeric hydroxy group involvement: Specify if an alpha or beta anomeric carbon was used based on its position on the ring (3:00 on a clock).

Case Study: Lactose

• Components: Beta D-galactose + beta D-glucose.
• Linkage: Typically, the C1 of galactose links to C4 of glucose, resulting in a beta 1 to 4 linkage.
  • Hydroxyl group contributions: Hydroxyl from C1 of galactose and C4 of glucose.
• Glycosidic Bond: Link between monosaccharides through a glycosidic bond (a type of covalent bond).
• Biological Function: Provides energy for nursing infants (milk sugar).

Examples of Other Disaccharides

1. Sucrose (Table sugar):
   • Formed from alpha D-glucose and beta D-fructose.
   • Linkage: C1 of glucose and C2 of fructose (alpha 1 to beta 2).
   • Biological function and storage form in plants.
2. Maltose (Malt sugar):
   • Formed from two alpha D-glucose linked at C1 and C4 (alpha 1 to 4 linkage).
3. Isomaltose:
   • Formed from alpha D-glucose linking C1 to C6 (alpha 1 to 6 linkage) on two glucose units.
4. Mannobios:
   • Formed from two D-mannose units linked at C1 and C3 (alpha 1 to 3 linkage).

Conclusion

• Various disaccharides exhibit different linkages and biological functions based on their monosaccharide components.
• The specific carbons used in linkages and whether they are alpha or beta are crucial for their identification and function in biological contexts.