Understanding Carbohydrates and Their Types

Sep 11, 2024

Carbohydrates: Overview

Key Points

  • Carbohydrates are the most abundant biomolecules on Earth.
  • Major source of energy for all living organisms (animals and plants).
  • Serve as structural components (e.g., DNA contains ribose; plant cell walls made of cellulose).
  • Composed mainly of carbon, hydrogen, and oxygen (C:H:O ratio = 1:2:1).

Types of Carbohydrates

  • Four main types:
    • Monosaccharides
    • Disaccharides
    • Oligosaccharides
    • Polysaccharides

Monosaccharides

  • Smallest units of carbohydrates; also known as simple sugars.
  • Main monosaccharides in the human diet:
    • Glucose
    • Galactose
    • Fructose
  • Structure of Glucose:
    • 6 carbon atoms (C1, C2, C3, C4, C5, C6).
    • Exists in alpha and beta forms:
      • Alpha Glucose: Hydroxy group on C1 opposite to C6.
      • Beta Glucose: Hydroxy group on C1 same direction as C6.

Disaccharides

  • Formed from two monosaccharides linked together.
  • Examples:
    • Maltose: Two alpha glucose molecules linked by an alpha 1,4 glycosidic bond (condensation process).
    • Lactose: Galactose + Glucose linked by a beta 1,4 glycosidic bond (found in milk).
    • Sucrose: Glucose + Fructose linked by an alpha 1,2 glycosidic bond (table sugar, plants produce it).

Oligosaccharides

  • Short chains of monosaccharides (typically less than 20).
  • Example: Adding a glucose to maltose creates Maltotriose (three glucose units).

Polysaccharides

  • Long chains of monosaccharides (more than 20 units).
  • Two types:
    • Homopolysaccharides: Only one type of monosaccharide (e.g., starch, glycogen).
    • Heteropolysaccharides: Two or more types of monosaccharides.

Examples of Polysaccharides

  1. Starch:
    • Storage form in plants.
    • Composed solely of glucose.
    • Can be branched (amylopectin) or unbranched (amylose).
  2. Glycogen:
    • Storage form in animals.
    • Similar structure to starch but with more frequent branching (every 8-12 glucose residues).
  3. Dextrans:
    • Structural polysaccharides in bacteria and yeast.
    • Contains various glycosidic bonds (e.g., alpha 1,2, alpha 1,6).
  4. Cellulose:
    • Structural component in plants (plant cell walls).
    • Unbranched homopolysaccharide of beta glucose.
    • Linked by beta 1,4 glycosidic bonds (humans cannot digest cellulose).

Summary

  • Carbohydrates are crucial for energy and structure in living organisms.
  • Understanding the types and structures of carbohydrates aids in studying biochemistry.