• 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.