A-LEVEL NOTES
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A-LEVEL NOTES

A-LEVEL BIOLOGY OCR NOTES 
enzymes


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Enzymes
  • Enzymes are biological catalysts that speeds up the rate of reaction and remains unchanged and reusable at the end of the reaction.
  • They lower the activation energy of the reaction.
  • ​The lock and key model proposed that each substrate is a key that only fits a specific lock or enzyme. The alternative induced fit model has been proposed (below)
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  • The specificity of enzymes is due to the tertiary structure of its active site, allowing complementary binding to substrates.
  • Enzymes catalyse both intracellular and extracellular reactions that determine structures and functions from cellular to whole organism level.
    • Catalase intracellularly breaks down hydrogen peroxide into water and oxygen
    • Amylase is secreted from the salivary glands and pancreas to extracellularly break down starch. Requires Cl- cofactor
    • Trypsin is secreted from the pancreas to extracellularly break down proteins
  • Some enzymes are synthesised in an inactive precursor form and need to be activated e.g. another enzyme removes part of the molecule in trypsin, forming the correct active site shape
  • Some enzymes require a cofactor, which is a substance which must be present to enable an enzyme to catalyse a reaction at the appropriate rate.
    • A prosthetic group is permanently bound e.g. Zn^2+ bound to carbonic anhydrase                         CO2 ⟷ H2CO3 ⟷ H^+ + HCO3
    • A coenzyme forms temporary associations and are derived from vitamins.
  • Factors affecting enzyme activity include:
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  • The temperature coefficient (Q10) for a specific reaction is the effect of a 10°C rise in temperature on the rate of the reaction
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