Enzymes

• What are enzymes?

  Biological catalysts produced by living things
• Why do living things produce enzymes?

  To speed up useful chemical reactions inside a living creature
• How can you make a reaction happen more quickly in living organisms?

  By raising the temperature before cells start to be damaged
• What is a catalyst?

  A substance that increases the speed of a reaction without being changed or used up
• Why do enzymes have specific shapes?

  Because they need to fit onto the substances involved in reactions
• What are the key characteristics of enzymes?

  • Enzymes have an active site with a unique shape
  • They usually catalyse one specific reaction
  • The substrate must fit into the active site for the reaction to occur
  • If the substrate doesn't match, the reaction can't be catalysed
• What is the "lock and key" model of enzyme action?

  It describes how the active site fits the substrate like a key fits a lock
• What is the "induced fit" model of enzyme action?

  It describes how the active site changes shape slightly as the substrate binds
• How does temperature affect enzyme-catalysed reactions?

  Changing the temperature changes the rate of the reaction
• What happens to an enzyme if the temperature gets too high?

  The enzyme's active site changes shape and it becomes denatured
• What is meant by an enzyme being denatured?

  It means the enzyme's shape has changed and it can no longer function
• What is an optimum temperature for enzymes?


  It is the temperature at which an enzyme works best
• How does pH affect enzyme activity?

  A pH that is too high or too low can denature the enzyme
• What is the optimum pH for most enzymes?

  Often neutral pH 7, but not always
• What is the optimum pH for pepsin?

  pH 2, which is suited to acidic conditions in the stomach
• Enzyme inhibitors can be competitive or non-competitive.