Biol 1 - Enzymes

AQA AS Biol 1 notes on Enzymes

  • Created by: Stephanie
  • Created on: 10-05-12 20:05

Enzyme Action

  • A biological catalyst
  • Protein
  • Active Site has specific shape so highly specific 

Reduces activation energy needed for a reaction

  • If joining, holding two substrates close together reduces repulsion
  • In breakdown (lysis) fitting to active site puts strain on bonds 
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Lock & Key Model:

  • No longer so widely accepted
  • Says substrate fits enzymes active site like a key to a lock

Induced Fit Model:

  • Substrate doesn't just need complementary shape - needs to induce enzyme to change active site shape
  • So substrate is locked more tightly
  • More accepted theory - explains why so specific
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Factors effecting Enzyme Activity


  • More heat = more kinetic energy, so reaction speeds up (more collisions)
  • To a point - temp too high can denature the enzyme 


  • Optimum pH (usually 7)
  • Above and below H and OH ions can interfer with ionic hydrogen bonds and denature enzyme

Substrate concentration:

  • Higher substrate conc.= faster reactions (more collisions)
  • Up to a saturation point 
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