Biol 1.1

• Very crude generalization:
• The main 6 elements of life C, H, O, N, P, and S generally account for >95% of the elemental composition of living organisms
• Life is mostly water
• Composition of Anabaena variabilis cell

  • 20% Carbohydrates
  • 10% Lipids
  • 36% Proteins
  • 25% Nucleic acids
  • 5% Mixed macromolecules
  • 3% Cofactors
• Composition of Escherichia coli cell

  • 2% Carbohydrates
  • 9% Lipids
  • 55% Proteins
  • 24% Nucleic acids
  • 6% Mixed macromolecules
  • 3% Cofactors
• Inorganic ions in Anabaena variabilis

  • Na+
  • Cl-
  • K+
  • Fe++
  • Mg++
  • Zn++
  • Cu++
  • Others
• Organic molecules contain carbon (C)
• A broad (but not exhaustive) definition of an organic compound includes any molecule with C—H or C—C bonds (covalent)
• Why is life carbon-based?

  • Has a valence of 4
  • Can form chains and rings
  • Is abundant on Earth
• Earth's crust composition
• Monomer


  Units that are linked together to form larger organic molecules
• Polymer


  Many monomers linked together
• Synthesis of larger organic molecules

  1. Monomers

  2. Dimer

  3. Oligomer

  4. Polymer
• The dehydration reaction occurs during synthesis
• Branched polymer formation is possible if there are suitable branching points
• Hydrolysis occurs during breakdown of polymers