Enzymes

• The lock and key diagram is a simple model to explain the action of enzymes.
• Enzymes are protein molecules , with complex shapes which are important for their activity :

  • Part of an enzyme molecule is its active site
  • A substrate molecule fits into the active site - like a key fits into a lock
  • Other substances do not fit so are not substrates for that enzyme
  • If the shape of an active site changes the enzyme is denatured and no longer works
• Is a lock and key diagram

  
• Enzymes are protein molecules
• Enzymes are affected by temperature and pH
• Effect of temperature on enzymes:

  
  

  As the rate of chemical reactions increase so does the temperature. This happens with enzyme-catalysed reactions but:

  • There is an optimum temperature at which there is a maximum reaction rate.
  • At higher temperatures the active site changes shape , reducing the reaction rate.
• This is a graph showing the effect of temperature on enzymes

  
• A shows ( the peak going up ) heat energy causing more collisions between enzymes and the substrate.

  
• Effect of PH on enzymes :

  The PH of an enzymes surrounding affects the shape of the active site. This means that:

  • Enzymes have an optimum PH at which there is a maximum reaction rate
  • Below and above the optimum PH the bonds in the enzyme are also affected, so the shape of the active site changes
• This is a lock and key diagram