MLB 133

• Age of Earth: 4.5 billion years
• There was no life 4 billion years ago
• Atmosphere

  Made of water vapour & gases
• Was CO2 prevalent (common) in the primitive atmosphere? If not, why? Refer to Theme 2
• Bombardment


  The primitive atmosphere was continuously bombarded by UV, volcanic heat, radioactive decay & lightning

  
• The reactions led to the formation of first carbon-based molecules (origin of life, Theme 2)
• First cells (protobionts) were eventually formed from the carbon-based (organic) molecules created under the condition of the primitive Earth
• Life as we know it, is dependent on carbon-based (made up of carbon atoms) molecules
• Abiogenesis hypothesis

  The hypothesis that was tested in the Miller's experiment
• Miller's experiment


  1. Reactants

  2. Significance of methane

  3. Reactant that can substitute methane

  4. Products

  5. Source of energy

  6. Type of reaction

  7. Use of closed apparatus

  8. Conclusion
• Cells are 70–95% water, the rest consists mostly of carbon-based compounds
• Carbon


  Unparalleled in its ability to form large, complex, and diverse molecules

  
• Molecules that distinguish living matter from non-living matter

  • Proteins
  • Nucleic acids
  • Carbohydrates
  • Lipids
  • Other carbon-based molecules
• Carbon-based compounds/molecules


  Organic compounds/molecules = Macromolecules
• Differences between inorganic and organic molecules

  • Inorganic molecules usually contain positive & negative ions
  • Inorganic molecules usually have ionic bonding
  • Inorganic molecules are usually associated with non-living matter
  • Organic molecules always contain carbon & hydrogen
  • Organic molecules always have covalent bonding
  • Organic molecules may be quite large with many atoms
  • Organic molecules are usually associated with living organisms

  
• Inorganic molecules

  • C2H2NO
  • H3PO2
  • H2SO4
  • CaCl2
  • H2O
• Organic molecules


  • C2H4
  • C2H4O2
• Organic compounds are not found only in living things
• Electron configuration


  Indicates the kinds & number of bonds an atom will form

  
• Ways to illustrate electron configuration

  • Electron shell diagram
  • Electron orbital diagram
• Carbon has 4 valence electrons (tetravalent) – it can form 4 covalent bonds

  
• Carbon and silicon


  Belong to the same group, expected to have the same chemical properties
• Reasons why the evolution of organic molecules favoured carbon and not silicon

  • Carbon forms strong covalent bonds
  • Carbon can form diverse structures

  
• Covalent bonds


  Relatively strong bonds compared to ionic bonds or Van der Waals forces
• Carbon-to-carbon bonds (covalent) are very strong & not easily broken

  
• Carbon-to-carbon bonds are not limited to single bonds, double & triple bonds may be formed. Ring compounds of biological significance may be formed

  
• Intersection points from which molecules can branch off in 4 directions are possible, thereby creating structural formulas with various shapes & lengths
• Molecular formula


  Chemical symbols for the constituent elements followed by numeric subscripts indicating the actual numbers of each type of atom per molecule
• Structural formula


  Shows the types, numbers & arrangement of atoms in a molecule

  
• Empirical formula


  The simplest whole number ratio of the atoms in a compound
• Hydrocarbons


  Organic molecules consisting of only carbon & hydrogen
• Covalent bonds between C & H are energy-rich – may be broken to release energy in cells
• 1. H & C-C bonds are evenly distributed (non-polar covalent bonds). They have comparable (same) electronegativity

  
• Hydrocarbons are considered to be less diverse
• Hydrocarbons


  Non-polar molecules (hydrophobic) that are not attracted to water
• Many organic molecules, such as fats, have hydrocarbon components. That is, hydrocarbons are not found in living things as individual (separate) molecules, but bonded (attached) to other polar molecules
• Hydrocarbons can undergo reactions that release a large amount of energy
• Isomers


  Compounds with the same molecular formula but different structures and properties
• Types of isomers


  • Structural isomers
  • Stereoisomers
  • Optical isomers
• Structural isomers have the same molecular formula, but different arrangements of the atoms in the molecule