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