Lecture Notes: Carbohydrates - The First Macromolecule Type

Overview of Carbohydrates

• Common examples include bread, pasta, cake, fruits (apples, pears, grapes, strawberries).
• Found in grains, fruits, vegetables.
• Provide energy via glucose molecules.
• General formula: Carbon (C) : Hydrogen (H) : Oxygen (O) = 1:2:1 (e.g., glucose is C6H12O6).

Types of Carbohydrates

1. Monosaccharides

   • Single sugar molecules.
   • Carbon chain length of 3 to 7 carbons.
   • End with "ose" (e.g., glucose, sucrose, fructose).
   • Contain carbonyl groups:
     • Aldoses: Carbonyl group with hydrogen attached.
     • Ketoses: Carbonyl group with carbon attached on both sides.
   • Classification based on carbon chain length:
     • 3 carbons: Trioses
     • 5 carbons: Pentoses
     • 6 carbons: Hexoses
   • Structural isomers: Same chemical formula, different structure (e.g., glucose, galactose, fructose).
   • Can exist in linear and ring forms (usually ring in aqueous solutions).
   • Ring structures categorized by the position of hydroxyl group:
     • Alpha: Hydroxyl below carbon 1
     • Beta: Hydroxyl above carbon 1

2. Disaccharides

   • Formed by two monosaccharides via a dehydration reaction.
   • Linked by glycosidic bonds (covalent bonds).
   • Common disaccharides:
     • Maltose: Two glucose molecules.
     • Lactose: Galactose + glucose (found in milk).
     • Sucrose: Glucose + fructose (table sugar).
   • Linkage types:
     • Alpha glycosidic bond (e.g., alpha 1-2 linkage).
     • Beta glycosidic bond (if hydroxyl was above carbon).

3. Polysaccharides

   • Many monosaccharides linked together.
   • Can be branched or unbranched.
   • Examples:
     • Starch: Plant energy storage, made of glucose.
     • Glycogen: Animal energy storage, highly branched.
     • Cellulose: Found in plant cell walls, linear structure, made of beta 1-4 linkages.
     • Chitin: Found in exoskeletons of arthropods and fungal cell walls, made of N-acetyl-beta-D-glucosamine.

Important Concepts

• Structural Isomers: Molecules with the same molecular formula but different structures.
• Glycosidic Bonds: Covalent bonds linking sugar molecules.
• Ring Structures: Monosaccharides can form ring structures in aqueous solutions.
• Energy Storage:
  • Plants: Starch and cellulose.
  • Animals: Glycogen.
  • Fiber: Composed mostly of cellulose, indigestible by humans.

Biological Significance

• Digestion:
  • Humans can digest starch and glycogen but not cellulose (requires cellulase enzyme present in some herbivores).
  • Termites rely on gut microbes for cellulose digestion.
• Chitin: Provides structural support in exoskeletons and fungi.

Next Topic

• Upcoming lecture will cover lipids, the second type of biological macromolecule.