enzymes

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  • Enzymes
    • competitive inhibitors
      • binds to the active site
      • prevents the substrate from binding
      • slows down rate of reaction
      • effect is often reversible
      • e.g  the use of ethanol foranti freeze
        • if taken into the body the liver breaks it down into alcohol dehydrogenase which in the liver breaks down to oxalic acid
        • the ethanol competitively inhibits alcohol dehydrogenase so that less oxalic acid is formed
    • non competitive inhibitors
      • binds to the alllosteric site on the enzyme
      • changes the shape of the active site
      • prevents the substrate from binding
      • effect is often irreversable
      • e.g potassium cyanide
        • inhibits cell respiration
        • non competitive inhibitor for the enzyme cytochrome oxidase
        • ATP cannot be made
        • organism respires anaerobically so lactic acid builds up in the blood
    • coenzymes
      • organic non protein molecules
      • bind either just before or at the same time as the substrate
      • may take part in the reaction but are reformed
      • carry chemical groups between enzyme controlled reaction together
    • induced fit hypothesis
      • active site is cavity in which the substrate fits
      • initially the active site is not correct to fit the substrate
      • as the substrate approaches the active site changes shape to become complementary
      • after the reaction takes place and the products are gone the active site returns to its original shap
    • lock and key hypothesis
      • active site already exact complementary shape for substrate, like a lock and key
    • factors effecting rate of reaction
      • temperature
        • as temperature rises kinetic energy increases
        • more molecules move which increases rate of reaction
        • increases up to optimum
        • bonds are broken holding enzyme in correct strcuture
        • enzyme eventually denatures
      • PH
        • changes in PH can break bonds
        • this changes the 3D shape of the enzyme
        • fewer es complexes form
      • enzyme concentration
        • rate of reaction proportional to enzyme concentration
        • more es complexes formed increases chance of collisions
      • substrate concentraion
        • rate of reaction increases with increasing substrate concentration up to a point
        • the enzyme substrate concentration has to dissacoaite  before more substrate can bind
        • on a graph it rises to then level off
    • enzymes are...
      • speed up the rate of reaction
      • catalysts
      • are not chemically altered
      • only  a small amount needed to alter the rate
      • need to be in an aqueous solution as this allows the enzyme and substrate to move around
      • intracellular (inside cells)
      • extracellular (outside cells)
    • metabolism
      • catabloic respiration
        • substrate broken down e.g respiration
        • catalysed by enzymes
      • anabolic respiration
        • used to build a new molecule
        • formation of cellulose for cell walls
        • catalysed by enzymes
    • end product inhibition
      • stops reaction  at end as substrate cannot bind to active site

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