Enzymes

• Enzymes


  • Catalysts that speed up the rate of a chemical reaction without being changed or used up in the reaction
  • Proteins
  • Biological catalysts (biological because they are made in living cells, catalysts because they speed up the rate of chemical reactions without being changed)
  • Necessary to all living organisms as they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life
• Enzyme substrate specificity

  • Enzymes are specific to one particular substrate (molecule/s that get broken down or joined together in the reaction) as the enzyme is a complementary shape to the substrate
  • The product is made from the substrate(s) and is released
• Lock and key model of enzyme activity

  • Enzyme has a specific 3-D shape
  • Active site of the enzyme is a complementary shape to the substrate
• How enzymes work

  1. Enzymes and substrates randomly move about in solution

  2. When an enzyme and its complementary substrate randomly collide - with the substrate fitting into the active site of the enzyme - an enzyme-substrate complex forms, and the reaction occurs

  3. A product (or products) forms from the substrate(s) which are then released from the active site

  4. The enzyme is unchanged and will go on to catalyse further reactions
• Increasing the temperature from 0⁰C to the optimum


  Increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction
• Denaturation


  • Breaking the bonds that hold the enzyme together, causing it to lose its shape
  • Substrates cannot fit into denatured enzymes as the shape of their active site has been lost
  • Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop
• Optimum pH


  Most enzymes have an optimum pH of 7, but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)
• If the pH is too high or too low


  The bonds that hold the amino acid chain together to make up the protein can be destroyed, changing the shape of the active site so the substrate can no longer fit into it, reducing the rate of activity
• Moving too far away from the optimum pH


  Will cause the enzyme to denature and activity will stop