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  • 1. YEAR 12 - AS Biology 29 th November 2005 Enzymes dr shabeel pn
  • 2. Lesson Objectives
    • Enzyme unit overview
      • What are they?
      • How they work
        • Activation energy
      • What controls their activity
        • Rates of reaction
        • Substrate/enzyme concentrations
        • Temperature, pH
        • Enzyme inhibitors
      • Practical to demonstrate “Catalase” activity in different tissue samples
  • 3. Previous related topics covered?
    • Enzyme controlled reactions?
    • Proteins?
    • Lipase, protease, pectinase, amylase etc?
    • “ Lock & Key” molecular structures?
  • 4. By the end of the unit you should be able to:-
    • Explain enzymes as Globular Proteins which act as catalysts
    • Explain their catalytic action in terms of lowering activation energy
    • Describe examples of enzyme-catalysed reactions
    • Discuss factors affecting reaction rates and inhibition
    • Describe how to investigate these effects experimentally
  • 5.
    • Enzymes:-
      • Are defined as a BIOLOGICAL catalyst i.e. something that speeds up a reaction. Up to 10 12 fold
      • Usually end in ‘…ase’.
      • Discovered in 1900 in yeasts. Some 40,000 in human cells
      • Control almost every metabolic reaction in living organisms
      • Are globular proteins coiled into a very precise 3-dimentional shape with hydrophilic side chains making them soluble
      • Possess an active site such as a cleft in the molecule onto which other substrate molecules can bind to form an enzyme-substrate complex
      • Once the substrate has been either synthesised or split, enzymes can be re-used.
      • Do not ‘ create ’ reactions
      • Widely used in industrial cleaning
      • Often require co-factors (co-enzymes) to function – metal ions, or vitamin derivatives
  • 6.  
  • 7. Amylase + starch substrate
  • 8. How do enzymes work?
    • Reaction Mechanism
      • In any chemical reaction a substrate is converted into a product .
      • In an enzyme catalysed reaction the substrate first binds to the active site of the enzyme to form the enzyme-substrate complex
  • 9.  
  • 10. Molecule Geometry
    • Substrate molecule fits into the enzyme like a lock & key.
    • Enzyme shape distorts or it changes other factors to make the reaction happen
  • 11. “ Activation Energy”
    • In a ‘natural’ reaction the product has a lower energy than the substrate so equilibrium will take it in the direction of the product.
    • However there is an energy ‘barrier’ to be overcome
    • Enzymes lower the activation energy required to bring about a reaction.
    • EG catalase reduces the activation energy for the reduction of H 2 0 2 86-fold
  • 12.  
  • 13. Reaction rate factors
    • Substrate concentration
      • Initially rate increases with substrate conc.