CC4

• Enzymes are biological catalyst that speed up biological reactions by reducing the amount of activation energy. They are globular proteins that have a compact structure with a specific active site which is complementary to the substrate.
• Anabolic reactions involve building smaller molecules into larger molecules.
• Catabolic reactions are reactions that break down larger molecules into smaller molecules.
• What are catabolic reactions?


  Breaking down larger molecules into smaller molecules.
• What are anabolic reactions?

  Building smaller molecules into larger molecules.
• Intracellular enzymes are produced and used inside the cell.
• Extracellular enzymes are secreted outside of the cell
• Name 2 models of enzyme action

  • Lock and key
  • Induced fit
• Describe the lock and key model

  • Enzyme and substrate are complementary
  • When they bind they create an enzyme substrate complex
  • Bonds become unstable and a reaction occurs
  • Products leave the enzyme and are no longer complementary
  • Enzyme is left unchanged
• Describe the induced fit model

  • The enzyme and substrate are not complementary
  • When in close proximity they cause a change in each others shape allowing the enzyme to mould around the substrate
  • An enzyme substrate complex is formed
  • Bonds become unstable causing a reaction
  • Products leave which are no longer complementary to the enzyme and the enzyme returns to its original shape
• Name 4 factors that affect enzyme action

  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration
• Temperature: Describe A


  As temperature increases, rate increases because the molecules have more kinetic energy so move faster. This causes more frequent successful collisions to occur which means more enzymes substrate complexes form.

  
• Temperature: Describe B

  B is the optimum temperature which in humans is 37 degrees. This shows the maximum enzyme activity.

  
• Temperature: Describe C


  As temperature increases above the optimum, rate decreases. This is because bonds in the enzyme active site break causing the active site to change shape. This means the enzyme is no longer complementary to the substrate so enzyme substrate complexes cant form. The enzyme is said to be denatured.

  
• pH: Describe the graph

  • Enzymes function in narrow ranges
  • Small deviations from the optimum can cause reversible reactions
  • Large deviations from the optimum cause bonds in the active site to break. This means the active site changes shape and is no longer complementary to the substrate. The enzyme is said to be denatured.

  
• Substrate concn: Describe A

  As concentration increases, the rate increases because more enzyme substrate complexes can form.

  
• Substrate concn: Describe B

  As concentration incraeses, rate plateus because all the active sites are full. So adding more substare wont make a difference and less enzymes substrate complexes will form. The enzyme is the limiting factor.

  
• Enzyme concn: Describe A

  As enzyme concentration increases, the rate increases. This is because more enzymes mean more enzyme substrate comeplexes can form.

  
• Enzyme concn: Describe B

  As enzyme concentration increases, the rate plateus because there is not enough substrate to fill all the enzyme active sites. This means no more enzyme substrate complexes can form. The substrate is the limiting factor

  
• When enzymes denature, the atoms in the active site vibrate. This causes hydrogen bonds to breaks which means the active site changes shape. The enzyme is no longer complementary to the substrate.
• Name 2 types of inhibitors

  • Competitive
  • Non-competitive
• Competitive inhibitors are comeplementary to the enzyme so compete with the substrate for the active site. When it binds it stops the substrate from binding so less enzyme substrate complexes form. Adding more substrate will overcome this due to more frequent successful collisions.
• Competitive inhibitors

  • Comeplementary to the enzyme
  • Compete with the substrate for the active site.
  • Stops the substrate from binding so less enzyme substrate complexes form.
  • Adding more substrate will overcome this due to more frequent successful collisions.
• Non-competitive inhibitors are not complemetary to the enzyme but instead bind to the allosteric site. This causes the active site to change shape so no substrate can bind. This reduces the amount of enzyme substrate complexes that can form.
• Non-competitive inhibitors

  • Not complemetary to the enzyme
  • Bind to the allosteric site.
  • Causing the active site to change shape so no substrate can bind.
  • This reduces the amount of enzyme substrate complexes that can form.
• Immobilised enzymes are enzymes that cannot move and are attached to an inert support.
• Name 2 methods of immobilising enzymes

  1. Entrapment/Encapsulating in sodium alginate bead
  2. Binding/Crosslinking with cellulose fibres
• Name an example of entrapment

  Clinistix
• Clinistix tests for glucose in urine. The stick has a cellulose pad which contains the immobilised enzymes.
• Name an example of crosslinking immobilised enzymes with cellulose fibres

  Biosensors
• Biosensors test blood glucose levels.
• Name 4 advantages of using immobilised enzymes

  • Can be separated to be reused and so that the product isnt contaminated with enzymes that people may be allergic to.
  • They are more stable so are less affected by temperature and pH and work over a larger range of values
  • It creates a barrier between the enzyme and the environment
  • Reactions can be carried out at higher temperatures so there are faster rates of reaction
• Name 2 disadvantages of imoboilised enzymes

  • Enzymes need imobilising which requires more time, money and chemicals
  • Imobilisation may make it harder for enzyme substrate complexes to form as the maximum rate of reaction is lowered due to them being able to work at a wider range of values