Lecture 3 Notes

Key Concepts in Carbohydrate Chemistry

1. Redox Reactions

  • Redox Chemistry: Involves oxidation-reduction reactions where:
    • Oxidation: Gain of oxygen or loss of hydrogen.
    • Reduction: Loss of oxygen or gain of hydrogen.
  • Monosaccharides: Can participate in redox reactions, being categorized as either reducing or non-reducing sugars.

2. Oxidation of Sugars

  • Aldehydes: May be oxidized to carboxylic acids.
    • Example: D-glucose (aldose) can be oxidized to gluconic acid (aldonic acid).
  • Reducing Sugars: These sugars can react with Benedict's or Tollens' reagents due to their ability to reduce metal ions (Cu²⁺, Ag⁺).

3. Reducing Sugars and Tests

  • Benedict's Test:
    • Detects reducing sugars by reducing Cu²⁺ to Cu⁺, forming a colored precipitate.
  • Tollens' Test:
    • Silver ion (Ag⁺) is reduced to metallic silver when reacting with reducing sugars.

4. Rearrangement of Sugars

  • Ketoses: Under basic conditions, ketoses can rearrange to form an aldose (a reducing sugar).
  • Both aldoses and ketoses react with Benedict's and Tollens' reagents to form aldonic acids.

5. Glycosidic Linkages

  • Types: Glycosidic linkages can be differentiated as alpha (α) or beta (β) based on the orientation of the anomeric carbon.
  • Significance: This orientation influences the biological function and digestibility of carbohydrates.
    • Examples: Maltose has an α(1→4) linkage, while cellulose has a β(1→4) linkage leading to different properties.

6. Polysaccharides

  • Monomers: Glucose is the monomer unit for common polysaccharides like starch and cellulose.
  • Structure:
    • Starch: Consists of amylose (linear) and amylopectin (branched).
    • Cellulose: A linear polymer with extensive hydrogen bonding, making it water-insoluble.
  • Energy Storage vs. Structural Role:
    • Starch and glycogen serve as energy reserves, while cellulose provides structural integrity to plants.

7. Digestion of Carbohydrates

  • Enzymatic Breakdown: Starch and glycogen are hydrolyzed by enzymes like amylase into simpler sugars (maltose, glucose).
  • Lactose Intolerance: Occurs due to the inability to produce lactase, leading to difficulties digesting the disaccharide lactose due to a specific glycosidic bond.

8. Blood Types and Oligosaccharides

  • Oligosaccharides: Short chains of sugars that can serve as antigens in blood.
  • Examples: Type A and B blood types differ due to the presence or absence of specific sugar modifications on the blood cell surfaces (N-acetylgalactosamine for A, galactose for B).