Chemical Basis of Life

Carbohydrates Overview

  • Carbohydrates are essential biomolecules that serve as a primary energy source for living organisms.

  • Main categories: Monosaccharides, Disaccharides, and Polysaccharides.

Types of Carbohydrates

Monosaccharides

  • Simplest form of carbohydrates consisting of single sugar units.

  • Examples: Glucose, Fructose, Galactose.

  • Characteristics: Sweet taste, soluble in water.

Disaccharides

  • Formed when two monosaccharides combine.

  • Examples: Sucrose, Lactose, Maltose.

  • Characteristics: Sweet taste, soluble in water.

Polysaccharides

  • Complex carbohydrates made of long chains of monosaccharide units.

  • Examples: Starch, Glycogen, Cellulose.

  • Characteristics: Generally not sweet, insoluble in water.

Significance of Carbohydrates in Living Organisms

  • Energy Source: Provides energy through cellular respiration.

  • Storage Compounds: Starch in plants and glycogen in animals serve as energy reserves.

  • Structural Components: Present in plant cell walls (cellulose).

  • Components of Nucleic Acids: Pentose sugars as constituents.

Testing for Carbohydrates

Starch Test

  • Reagent: Iodine solution.

  • Procedure:

    • Prepare starch solution from a food sample (e.g., potato).

    • Add iodine solution.

    • Observation: Color change to blue-black indicating presence of starch.

Glucose Test

  • Reagent: Benedict’s solution.

  • Procedure:

    • Prepare glucose solution.

    • Heat with Benedict’s solution.

    • Observation:

      • Initially blue (no reaction with sucrose).

      • Upon hydrolysis (with sulfuric acid), color changes from blue to green, yellow, orange, and finally brick red indicating glucose presence.

Summary of Carbohydrate Tests and Properties

  • Iodine Test for Starch:

    • Reddish-brown iodine turns blue-black with starch.

  • Benedict’s Test for Glucose:

    • No color change with sucrose; hydrolysis enables color change indicating glucose.

Conclusion

  • Carbohydrates are crucial for energy, storage, structure, and serve as components in various biological molecules, leading to their extensive presence and significance in living systems.