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  • Enzymes
    • basics
      • enzymes are biological catalysts, speed up chemical reactions, but are not used up themselves
      • enzyme action can me intracellular (inside cell) or extracellular (outside cell)
      • for enzyme reaction to work, subbstrate has to fit into active site, by the shapes being complementary. this forms an enzyme-substrate comnplex
    • models
      • 1: lock and key- substrate fits into active site the same way a key fits into a lock, the shapes are complementary.
      • 2:induced fit- temporary bonds form between R groupnof the amino acid and the substrate. the substrate makes active site change shape to make it fit more closely, reducing activation energy as it is under pressure
    • factors affecting
      • temperature: increase in temp increases kinetic enrgy, increases chance of collisons. after 40 degrees, active sites de nature.
      • pH: at low pH they denature as h+ ions break in H bonds. at high pH OH- break H bonds also, causing denature
      • substrate concerntration increase means more chance of collisions. eventually all active sites will be filled so concerntration of substrate will have no effect
      • enzyme concerntrationincreased chance of collions with greater concerntration, when all available substrates are being broken down enzyme concerntration wont make a difference
    • inhibitors/ poisons
      • competitive inhibitors: bind to active site as have complementary shape. stops substrate from binding.
        • increased substrate concerntration increases chances of substrate enzyme collisions
      • non- competitive inhibitors: bind to other area on enzyme and alter H bonds by h. phobic interations.  active site no longer complementary to substrate
        • increase in substrate concerntration has no affect as they cannot bind
      • in-organic co-factors: help enzyme and substrate to bind, arent used up,,
      • organic/ co enzymes: act as carriers, moving chemicals between different enzymes, they are constantly recycled
      • metabolic poisons- interfere with metabolic reactions.
        • EG cyanide- non competitive inhibitor of cytochrome C, this stops respiration of cells.
      • drugs:npenecillin inhibits enzyme transpeptidase which catalyses formation of proteins in bacterial cell walls, bacteria then cant controll osmotic pressure and burst
    • rates of reaction
      • a chemical needs a certain amount of energy for it to happen- activation energy
      • enzymes reduce the amount of activation energy needed and so speeds up the reaction
      • 1: enzymes hold 2 substrates close together reducing repulsion, helping them bond more easily
      • 2:fitting into active site puts a strain on the bonds in substrate and so breaks down more easily


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