Structure of enzymes

• All enzymes are

  Tertiary globular proteins
• Enzymes are

  Specific
• The substrate molecule binds to the active site of the enzyme to form an

  Enzyme-substrate complex
• The lock and key hypothesis suggests that

  There is an exact fit between the substrate and the active site of the enzyme
• Enzymes remain ... in reactions

  Unaltered
• Activation energy is the

  Minimum amount of energy required for a reaction to occur
• Enzymes ... the activation energy


  Lower
• Enzymes that build larger products from smaller substrate molecules are

  anabolic
• Enzymes that break large substrate molecules into smaller products are

  Catabolic
• Lock and key theory

  1. Enzyme + substrate meet each other
  2. Form an enzyme-substrate complex
  3. Catalysis occurs
  4. Form an enzyme-product complex
  5. Break into enzyme and product
• Induced fit hypothesis

  1. Substrate enters active site of enzyme
  2. Active site changes shape slightly as substrate binds
  3. Products leave active site of enzyme
• The charges on the amino acid side-chains of the active site must attract charges on the substrate molecule

  To form an enzyme substrate complex
• The charges of the enzymes active site are affected by

  Free hydrogen and hydroxyl ions
• The enzyme and substrate molecules move around more quickly due to an increase in kinetic energy. The chance of successful collisions between substrates and the enzymes active site increase, which leads to the formation of more enzyme substrate complexes.

  When temperature is increased
• If the temperature increases past the optimum temperature

  1. Atoms in the enzyme gain kinetic energy
  2. Hydrogen bonds are broken
  3. The tertiary structure unravels and the active site shape changes
  4. The active site is no longer complementary to the substrate
  5. No enzyme substrate complexes can be formed
  6. No product is made
• The optimum pH range of enzymes are

  Narrow
• Small changes in pH can...

  Affect the rate of reaction without affecting enzyme structure
• Small changes outside the optimum range of pH can...

  cause reversible changes in enzyme structure, inactivation of enzyme
• The pH affects the...

  Ionisation of the R-groups within the enzymes