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  • Catalysts are substances that speed the rate of chemical reactions and remain unchanged by the reaction.
  • In living organisms, the catalysts that speed up metabolic reactions are called enymes
  • Enzymes are protein molecules.
  • Enzymes are named according to the substrate on which they act; Proteases act on proteins, carbohydrases on carbohydrates, and lipases on fats (lipids)
  • Enzymes can break down large molecules into smaller ones, as well as, build up large molecules from smaller ones.
  • The active site on the enzyme is where the substrate binds for the reaction to take place.
  • Enzymes are very specific, so substrates bind to active sites that are complementary in shape to them. This is referred to as the ‘lock and key model’.
  • The substance that is produced by the reaction is called the product

Factors that Affect Enzyme Activity
  • Temperature
    • The optimum temperature for enzyme-controlled reactions is 37°C (body temperature)
    • As the temperature increases, the rate of reaction increases
    • But very high temperatures denature enzymes
  • pH
    • Different enzymes work best at different pH values.
    • At a pH higher or lower than the optimum pH decreases the enzyme activity.