enzymes

• Enzymes are globular proteins that increase the rate of reaction by lowering the activation energy of the reaction they catalyze
• The active site of an enzyme is where the reaction with the substrate takes place
• Each enzyme has a specific shape that must be complementary to the substrate, allowing only one type of substrate to fit into the active site of each enzyme (enzyme specificity)
• When the enzyme and substrate form a complex, the structure of the enzyme is altered so that the active site fits around the substrate, known as the induced fit model
• Enzymes can be intracellular (function inside cells) or extracellular, such as those used in digestion
• Lock and Key Theory (Fischer, 1894):

  • Active site and substrate have complementary shapes prior to binding
  • The enzyme binds with substrate forming an enzyme-substrate complex
  • Products are released from the active site and the enzyme can be reused
  • Only one substrate can fit each active site
• Induced Fit Theory (Koshland, 1958):

  • Enzyme has an active site
  • Enzyme is moulded around substrate as it enters to become complementary, forming an enzyme-substrate complex
  • Bonds form between oppositely charged groups on substrate and R groups to induce a better fit, putting a strain on the substrate molecule so reactions occur more easily
• Factors affecting the rate of enzyme-controlled reactions:

  • Enzyme concentration: rate increases as enzyme concentration increases, but beyond a certain point, increasing enzyme concentration has no effect on the rate of reaction
  • Substrate concentration: rate increases as substrate concentration increases, but beyond a certain point, the rate no longer increases as enzyme concentration becomes the limiting factor
  • Temperature: rate increases up to the optimum temperature, then decreases; very high temperatures cause denaturation
  • pH: as pH moves away from the enzyme's optimum, the rate of reaction decreases
• Factors affecting the rate of enzyme-controlled reactions (cont.):

  • Concentration of competitive reversible inhibitors: rate decreases as inhibitors block active sites temporarily
  • Concentration of non-competitive reversible inhibitors: rate decreases as the shape of the enzyme (not the active site) is altered by the inhibitors
• Investigating enzyme-catalyzed reactions:

  • Catalase: catalyzes the breakdown of hydrogen peroxide, measuring the rate of oxygen produced over time
  • Amylase: catalyzes the breakdown of starch, measuring absorbance over time to determine starch concentration
• Michaelis-Menten Equation: used to calculate the maximum rate of reaction (Vmax) by relating the velocity of enzyme reactions to the concentration of a substrate
• Immobilizing enzymes in alginate:

  • Enzymes are immobilized by attaching them to an insoluble, inert material like calcium alginate, enabling them to be reused
  • Immobilized enzymes are used in industry for continuous reactions and are more cost-effective than enzymes in solution