Enzymes

• Lock and key model: Enzymes are specific to their substrate and have a complementary shape to the substrate
• Enzymes

  Chemical substances that make living things work
• Enzymes

  • Are catalysts produced by living things
  • Living things have thousands of different chemical reactions going on all the time
  • Reactions need to be catalysed to get the right amounts of substances
  • Can make a reaction happen more quickly by changing the temperature
  • Enzymes reduce the need for high temperatures and only speed up useful chemical reactions in the body
• Enzyme active site

  The part where the enzyme joins on to its substrate to catalyse the reaction
• Enzymes

  • Usually only work with one substrate
  • Have high specificity for their substrate
  • Substrate has to fit into the active site for the enzyme to work
  • This is called the lock and key mechanism
• Factors affecting enzyme rate

  • Temperature
  • pH
  • Substrate concentration
• Increasing temperature

  Increases the rate of an enzyme-catalysed reaction at first
• Temperature getting too high

  Denatures the enzyme by changing the shape of the active site
• Enzyme denaturation

  When the shape of the enzyme's active site is changed, so the substrate can no longer fit
• Optimal temperature


  The temperature at which an enzyme works best
• Optimal pH


  The pH at which an enzyme works best
• Enzymes with non-neutral optimal pH

  • Pepsin in the stomach works best at pH 2
• Increasing substrate concentration

  Increases the rate of an enzyme-catalysed reaction up to a point
• Substrate concentration getting very high

  No further increase in rate as all enzyme active sites are full
• Rate of reaction is 1/time, so the rate of reaction is the number of reactions per unit time