Enzymes (organisation)

• An enyme is a biological catalyst; they speed up chemical reactions without being changed or used up.
• Explain the lock and key theory:

  
• Using the words "catalyst", "substrate" and "active site" label 


  the diagram below.

  
• Enzymes can only catalyse one specific reaction
• Every enzyme has an active site with a unique shape that fits onto the substrate.
• If the substrate does not fit into the enzyme's active site, the reaction won't be catalysed.
• The active site on an enzyme is where the substrate binds to form an enzyme-substrate complex (ES).
• Once the substrate is bound to the active site, the enzyme lowers the activation energy needed for the reaction to occur.
• Changing the temperature changes the rate of an enzyme-catalysed reaction.
• All enzymes have an optimum temperature that they work best, at 37 degrees celcius.
• The ph also affects enzymes. if it is too high or low, what happens to the enzyme?


  The enzyme's active site changes and it becomes denatured.
• What is the optimum ph? 


  Neutral 7.
• Give an example of an enzyme that does not perform best at 7:

  Pepsin - an enzyme used to break down protiens in the stomach. It works best at 2, meaning it is well suited to the acidic ph of stomach acid.
• Exam question: Explain why enzymes have an optimun pH. [2 marks]


  "If the ph is too high or low, it can interfere with the bonds holding the enzyme together. This changes the shape of the active site [1 mark] and denatures the enzyme [1 mark]."
• when an enzyme denatures, the active site changes shape and the enzyme can no longer perform its function.