Zoology Lecture Notes: Carbohydrates

Introduction

• Welcome by Steena Ma'am, Zoology Mentor.
• Discussion on syllabus completion and test schedules.
• Focus on carbohydrate chapter today.

Definition of Carbohydrates

• Carbohydrate means hydrates of carbon.
• General formula applicable for monosaccharides: CnH2nOn.

Classification of Carbohydrates

• Based on the number of sugar units:
  • Monosaccharides: Single sugar molecule (e.g., glucose, fructose, galactose).
  • Disaccharides: Two sugar molecules (e.g., lactose, maltose, sucrose).
  • Oligosaccharides: 2 to 10 sugar molecules (e.g., raffinose).
  • Polysaccharides: More than 10 sugar molecules (e.g., starch, glycogen, cellulose).

Reducing and Non-Reducing Sugars

• Monosaccharides are reducing sugars.
• Polysaccharides and some oligosaccharides are non-reducing sugars.
• Example: Sucrose is a non-reducing disaccharide.

Detailed Classification

Monosaccharides

• Cannot be hydrolyzed into simpler carbohydrates.
• Carbon atoms can range from 3 to 7.
  • Examples:
    • Triose: Glyceraldehyde, Dihydroacetone.
    • Tetroses: Erythrose, Erythulose.
    • Pentoses: Ribose, Xylose, Ribulose.
    • Hexoses: Glucose, Galactose, Fructose.
    • Heptoses: Glucoheptose, Pseudoheptulose.

Disaccharides

• Composed of two sugar units:
  • Examples:
    • Lactose: Glucose + Galactose.
    • Maltose: Glucose + Glucose.
    • Sucrose: Glucose + Fructose.

Oligosaccharides

• 3 to 10 sugar residues.
• Includes disaccharides and trisaccharides.

Polysaccharides

• Homopolysaccharides: Same sugar units (e.g., starch, glycogen).
• Heteropolysaccharides: Different sugar units (e.g., hyaluronic acid).
• Classification based on monomeric units:
  • Starch: Storage form in plants (alpha glucose).
  • Glycogen: Storage form in animals (highly branched alpha glucose).
  • Cellulose: Structural form in plants (beta glucose).

Glycosidic Bonds

• Formed between two sugar molecules through dehydration.
• Types of Linkages:
  • Alpha-1,4 Linkage: Between glucose units in starch.
  • Beta-1,4 Linkage: Found in cellulose.
  • Alpha-1,6 Linkage: Found in branching of glycogen.

Key Points on Specific Carbohydrates

• Starch: Comprises amylose (linear) and amylopectin (branched).
• Glycogen: Highly branched structure, stored in liver/muscle.
• Inulin: Made of fructose, kidney function test.
• Cellulose: Most abundant carbohydrate, indigestible by humans.

Heteropolysaccharides

• Examples include heparin and hyaluronic acid.
• Mucilage retains water, found in okra and aloe vera.

Conclusion

• Summary of carbohydrate types, structures, and functions.
• Next topic: Enzymes in the following session.
• Reminder for the burger quiz and a question of the day.