Enzymes

• what is activation energy?

  minimum amount of energy required to bring about a chemical reaction
• what is an enzyme?

  a protein that acts as a biological catalyst increasing the rate of a biological reaction. it does this by decreasing the activation energy
• what do enzymes catalyse?

  both intracellular and extracellular reactions
• what is an intracellular reaction?

  Reaction inside a cell
• what is an extracellular reaction?

  Reaction outside the cell
• what is an active site?

  the region on an enzyme where a substrate fits to catalyse a reaction
• how is the shape of the active site determined?

  by the enzyme's tertiary structure
• what is the induced-fit model of enzyme action?

  • first the substrate binds to the active site
  • then the shape of the active site changes so that the active site and substrate are complementary
  • this puts stress on the bonds in the substrate and makes it easier to break them
  • this lowers the activation energy
• what is a factor that affects enzyme-controlled reactions?

  enzyme concentration
• When the enzyme concentration is greater, there are more active sites available. This increases the probability of enzyme-substrate complexes forming.
• If the substrate is in excess, then increasing enzyme concentration increases the rate of reaction linearly
• what is a competitive inhibitor?

  an inhibitor that has a similar shape to the substrate and so binds to the active site of an enzyme
• what is a non-competitive inhibitor?

  inhibitors that bind to a different part of an enzyme and change the shape of the shape of that enzyme. this prevents enzyme-substrate complexes to form
• what is a factor that affects the rate of enzyme-controlled reactions?

  Temperature
• how does temperature affect the rate of enzyme-controlled reactions?

  • after the optimum temperature, increasing the temperature further causes hydrogen bonds in the enzyme to break
  • this changes the enzymes tertiary structure
  • when this happens, we say the enzyme is denatured
  • as more enzymes denature, the rate of reaction decreases
• what is a factor that affects the rate of enzyme-controlled reactions?

  pH
• what is pH a measure of?

  a solution's H+ concentration. the higher the concentration of H+ ions, the lower the pH of the solution
• how does pH affect the rate of enzyme- controlled reactions?

  • a change in pH breaks both the hydrogen and ionic bonds in an enzyme
  • this changes the enzymes tertiary structure
  • when this happens, we say the enzyme has denatured