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Carbohydrates: An Overview

Jul 14, 2024

Carbohydrates: The Most Abundant Biomolecules on Earth

Overview

  • Importance: Major source of energy for living organisms (animals and plants).
  • Structure Components: DNA (ribose), Plant cell wall (cellulose).
  • Composition: Carbon, hydrogen, and oxygen (1:2:1 ratio).

Types of Carbohydrates

  1. Monosaccharides
  2. Disaccharides
  3. Oligosaccharides
  4. Polysaccharides

Monosaccharides

  • Referred to as simple sugars.
  • Smallest units that make up carbohydrates.
  • Key Examples:
    • Glucose
    • Galactose
    • Fructose

Glucose

  • Main source of energy for humans.
  • Structure: Contains six carbon atoms.
    • Alpha glucose: Hydroxyl group at carbon-1 opposite to carbon-6.
    • Beta glucose: Hydroxyl group at carbon-1 same as carbon-6.

Disaccharides

  • Formed by two monosaccharides.
  • Examples:
    • Maltose: Two glucose molecules linked by alpha 1-4 glycosidic bond.
    • Lactose: Galactose and glucose linked by beta 1-4 glycosidic bond.
    • Sucrose: Glucose and fructose linked by alpha 1 (glucose) and beta 2 (fructose) glycosidic bond.

Oligosaccharides

  • Short chains of monosaccharides (less than 20).
  • Example: Maltotriose (three glucose molecules linked by alpha 1-4 glycosidic bonds).

Polysaccharides

  • Long chains of monosaccharides (more than 20).
  • Types:
    • Homopolysaccharides: Single type of monosaccharide.
      • Example: Glucose-only chains.
    • Heteropolysaccharides: Two or more different monosaccharides.

Storage Polysaccharides

  1. Starch (plants): Major carbohydrate in human diet.
    • Amylose: Unbranched chains of glucose linked by alpha 1-4 bonds.
    • Amylopectin: Branched chains with alpha 1-4 and alpha 1-6 bonds.
  2. Glycogen (animals): Similar to starch but more frequently branched.
    • Branched every 8-12 glucose residues.
  3. Dextrans: Structural component in bacteria and yeast:
    • Made of alpha 1-3 and alpha 1-6 bonds.

Structural Polysaccharides

  1. Cellulose: Main component in plant cell walls.
    • Unbranched chains of beta glucose linked by beta 1-4 glycosidic bonds.
    • Humans cannot digest cellulose due to lack of necessary enzymes.

Enzymatic Breakdown

  • Condensation: Forms bonds and releases water.
  • Hydrolysis: Breaks bonds by adding water.

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