Lecture Notes: Carbohydrates

Introduction

• Carbohydrates are one of the four classes of macromolecules.
• Serve as a food source for organisms and structural material for plants.

Chemical Structure

• Empirical formula: (CH_2O_n)
  • 'n' indicates the number of carbon atoms, ranging from 3 to over 1000.
• Types of carbohydrates:
  • Monosaccharides: Simple sugars, e.g., glucose, fructose.
  • Oligosaccharides: Small polymers of several monosaccharides.
  • Polysaccharides: Long chains, e.g., starch, glycogen.

Differences in Monosaccharides

1. Carbonyl Group Location
2. Number of Carbons
3. Spatial Arrangement of Atoms
   • Example: Hydroxyl group positioning.

Naming and Recognition

• Sugars end in "-ose" (e.g., pentose, hexose).
• Enzymes typically end in "-ase".
• Misconception: Carbohydrates are not carbon atoms bonded to water, rather contain carbonyl groups (aldehydes or ketones).

Chemical Reactions

• Dehydration Reactions: Join monosaccharides, forming disaccharides and polysaccharides, with the loss of water.
• Hydrolysis: Breaks down disaccharides back into monosaccharides.

Functional and Structural Aspects

• Sugars provide chemical energy and building blocks for other molecules.
• Hydrogen bonds make sugars reactive and hydrophilic.
• Distinct arrangements affect function (e.g., glucose vs. galactose).

Polymer Formation

• Disaccharides: Two monosaccharides linked (e.g., maltose from glucose).
• Polysaccharides: Thousands of monomers, function as energy storage or structural compounds.

Polysaccharide Examples

• Starch: Energy storage in plants, forms alpha-glucose chains.
• Glycogen: Energy storage in animals, similar structure to starch but more branched.
• Cellulose: Structural component in plant cell walls, made from beta-glucose, forms strong fibers.
• Chitin: Found in fungi and exoskeletons of insects, similar structure to cellulose but with N-acetylglucosamine.
• Peptidoglycan: Found in bacterial cell walls, most complex with alternating nag and nam units.

Biological Importance

• Carbohydrates provide structural materials, cell identity markers, and store chemical energy.
• Essential in forming nucleotides for DNA and RNA.

Conclusion

• Carbohydrates play a crucial role in the function and survival of living organisms.
• Next topic: Lipids.