Enzymes

• Enzymes

  Specific as their active site is only complementary to one substrate
• Enzymes

  • Tertiary structure proteins with a very specific 3D shape
  • Have an active site held together by peptide, hydrogen, ionic and disulphide bonds
• Lock and key theory

  Substrate fits exactly into the active site of the enzyme forming an enzyme-substrate complex, the reaction occurs and the products are released, the enzyme remains unchanged
• Enzymes

  • Intracellular (work inside cells)
  • Extracellular (secreted from cells for use outside of the cell)
• At low temperatures

  Low kinetic energy, few successful collisions where substrate enters active site
• As temperature increases

  Kinetic energy increases, more collisions and enzyme-substrate complexes formed per unit time, leading to increased product
• If temperature continues to increase

  Kinetic energy increases to a point where bonds holding 3D tertiary structure of active site are weakened, active site loses shape, enzyme is denatured
• At low substrate concentrations

  Substrate concentration is limiting the rate of reaction
• As substrate concentration increases

  Rate of reaction increases until all enzymes have full active sites, then enzyme concentration becomes the limiting factor
• Competitive inhibitors

  Complementary in shape to the active site, prevent formation of enzyme-substrate complexes by blocking the active site, do not bind permanently
• Non-competitive inhibitors

  Bind to the enzyme away from the active site, alter the shape of the active site so no enzyme-substrate complexes can be formed, some bind reversibly, others bind irreversibly
• Induced fit theory


  Active site and substrate are not fully complementary in shape, reactive groups align and substrate forces its way into active site, both areas change structure slightly, bonds in substrate weaken and reaction occurs at lower activation energy
• Enzymes

  Lower the activation energy of reactions but remain unchanged
• Small changes from optimum pH

  Make small reversible changes in enzyme molecule reducing its efficiency
• Large changes in pH

  Disrupt ionic and hydrogen bonds in enzyme causing permanent changes to shape of active site, preventing formation of enzyme-substrate complexes, denaturing the enzyme
• Immobilised enzymes

  • Increased stability, products uncontaminated, easily added/removed and recovered for re-use
• Uses of immobilised enzymes

  • Biosensors
  • Creating lactose-free milk
• Competitive inhibitors

  As substrate concentration increases, effect of inhibitor decreases as substrate collides more often with active site than inhibitor
• Increasing enzyme concentration

  Increases rate of reaction as more active sites are available
• Metabolism

  Anabolic reactions (building up molecules) and catabolic reactions (breaking down molecules) catalysed by enzymes
• Enzymes lower the activation energy of reactions
• Activation energy is the energy required to start a chemical reaction