Enzymes

• Enzymes


  Proteins which act as biological catalysts, speeding up reactions without being used up
• Enzymes


  • Tertiary, globular proteins that lower activation energy
• Reactions


  1. Anabolic - smaller, simple molecules are built up into larger, more complex molecules

  2. Catabolic - larger, complex molecules are broken down into smaller, simpler molecules
• How enzymes work


  1. Collide with substrate - bring into the correct orientation in active site

  2. E-S complex formed

  3. Bonds form between amino acids of the enzyme + molecules of the substrate

  4. E-P complex formed

  5. Products no longer fit the active site and are released
• Lock and Key


  Enzyme possesses an active site that is complementary to the substrate
• Enzyme specificity


  Only one type of substrate is catalysed by one type of enzyme
• Induced fit


  Shape of substrate will only be specific and complementary to a particular enzyme's active site
• As temperature increases


  Enzyme and substrate molecules have greater kinetic energy and so collide more, E-S complex formation increases
• As temperature increases further


  Activity increases to an optimum, then decreases and stops as the enzyme becomes denatured
• As temperature decreases below optimum


  Enzyme becomes inactive
• pH


  An enzyme will show maximum activity at an optimum pH, if pH is too acidic/alkali the enzyme will become denatured
• At lower substrate concentration


  Increase in substrate concentration increases rate of reaction
• As substrate concentration increases further


  Active sites become saturated, there are fewer free enzymes, rate of reaction is limited by substrate
• At lower enzyme concentration


  Increase in enzyme concentration increases the rate of reaction
• As enzyme concentration increases further


  Rate of reaction remains constant, enzyme activity is maximal
• Competitive inhibition


  Inhibitors compete with substrate for enzyme active site as they are similar shape
• Non-competitive inhibition


  Inhibitors bind elsewhere on the enzyme, block substrate from entering active site, prevent E-S complex formation, reduce enzyme activity
• Allosteric enzyme


  Possess a binding site away from the active site, regulate enzyme activity through negative feedback
• Co-factors


  Non-protein substances that enzymes require to function, include inorganic ions, prosthetic groups, and co-enzymes
• Biomarkers


  Some enzymes are only active during the disease process, detecting their presence can be used to diagnose a patient
• Immobilisation


  • Physically/chemically securing enzymes inside an inert and insoluble support material, increases thermostability and pH stability, enzymes can be retained and reused easily
• Immobilisation process


  May result in the active site changing shape, reducing binding of the substrate and reducing rate of reaction
• Biosensors contain immobilised enzymes, e.g. Clinistix for glucose, Albustix for protein, pregnancy tests
• Enzymes are sensitive to temperature, pH, substrate concentration, and enzyme concentration
• Enzymes show optimum activity at specific temperatures and pH values
• Increasing substrate or enzyme concentration increases the rate of reaction up to a point
• Competitive inhibitors bind to the active site, non-competitive inhibitors bind elsewhere on the enzyme
• Allosteric enzymes have a regulatory binding site away from the active site
• Co-factors are required by some enzymes to function
• Immobilising enzymes can increase their stability and allow reuse, but may reduce their activity
• Biosensors use immobilised enzymes to detect the presence of specific substances
• Adsorption 


  Enzymes are attached by weak forces to an inert substance
• Entrapment


  Enzymes are trapped within polymers
• Encapsulation 


  Enzymes are trapped inside a selectively permeable membrane
• Crosslinkage


  Enzymes are covalently bonded to a matrix. Enzymes may be covalently bonded to each other using linking chemicals