Biochemistry Lecture: Carbohydrates

Jul 15, 2024

Biochemistry Lecture: Carbohydrates

Overview

  • Carbohydrates: Most abundant biomolecules on Earth
    • Found in animals and plants
    • Source of energy
    • Structural components (e.g., DNA ribose, plant cell wall cellulose)
    • Composition: Carbon, hydrogen, oxygen (1:2:1 ratio)

Types of Carbohydrates

  1. Monosaccharides: Simple sugars (smallest units)
  2. Disaccharides: Made of two monosaccharides
  3. Oligosaccharides: Short chains of monosaccharides (up to 20)
  4. Polysaccharides: Long chains of monosaccharides (more than 20)

Monosaccharides

  • Key Examples: Glucose, Galactose, Fructose

Glucose

  • Main energy source for humans
  • Contains 6 carbon atoms
  • Two forms: Alpha glucose (OH group opposite C6) and Beta glucose (OH group same as C6)

Galactose + Fructose

  • Beta configurations (OH group same as C6)

Disaccharides

  • Formed via condensation reactions (release of water)
  • Broken down by hydrolysis (addition of water)

Examples

  1. Maltose: Glucose + Glucose (alpha 1,4 glycosidic bond)
    • Linked by alpha 1,4 glycosidic bond
  2. Lactose: Galactose + Glucose (beta 1,4 glycosidic bond)
    • Found in milk
  3. Sucrose: Glucose + Fructose (alpha 1, beta 2 glycosidic bond)
    • Table sugar formed by plants

Oligosaccharides

  • Short chains of monosaccharides
  • Example: Maltotriose (three glucose molecules, alpha 1,4 glycosidic bonds)

Polysaccharides

  • Also known as glycans
  • Can be homopolysaccharides or heteropolysaccharides
  • Storage forms: Found in plants, humans, bacteria

Examples

  1. Starch
    • Plant storage form
    • Two forms: Amylose (unbranched) and Amylopectin (branched)
    • Main human dietary carbohydrate
    • Bonds: Alpha 1,4 and Alpha 1,6 glycosidic bonds
  2. Glycogen
    • Animal storage form (similar to starch)
    • Branch points more frequent than in starch
    • Branching every 8-12 glucose residues
  3. Dextran
    • Structural component in bacteria and yeast
    • Contains alpha 1,3 and alpha 1,6 glycosidic bonds (also alpha 1,2 and alpha 1,4)
  4. Cellulose
    • Structural component in plants (plant cell wall)
    • Unbranched homopolysaccharide
    • Glucose molecules in beta configuration linked by beta 1,4 glycosidic bonds
    • Indigestible by humans due to lack of necessary enzymes