Enzymes

• What Are Enzymes?

  Enzymes are biological catalysts — they speed up chemical reactions without being used up themselves.
• Enzymes work by lowering the activation energy needed for a reaction to occur.
• Enzymes catalyse…

  both intracellular (inside cells) and extracellular reactions.
• What is a active site?

  An active site is the region on an enzyme where a substrate fits to catalyse a reaction.

   

  The shape of the active site is determined by the enzyme’s tertiary structure.
• Describe the induced-fit model of enzyme action.

  First, the substrate starts to bind 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 them easier to break.This lowers the activation energy.
• Describe the Lock and key model

  Lock and Key Model

  • The substrate fits into the enzyme's active site like a key fits into a lock.
  • The enzyme has a specific active site shape that only fits the correct substrate.
  • This model explains enzyme specificity, but it doesn't account for flexibility in the enzyme's shape.
• Enzyme Properties

  • Highly specific: Each enzyme catalyzes only one specific reaction (due to the unique shape of its active site).
  • Reusable: Enzymes aren’t used up in reactions—they can be reused multiple times.
  • Affected by environmental conditions: Temperature, pH, and substrate concentration can all affect enzyme activity.
• What factors can affect enzyme activity?

  Temperature

  pH

  substrate concentration

  Enzyme concentration

  Inhibitors
• Elaborate enzyme concentration

  • More enzymes mean more active sites available, increasing the rate of reaction.
  • But if substrate levels are low, increasing enzyme concentration will have no further effect (substrate becomes the limiting factor).
• Elaborate substrate concentration

  • Increasing substrate concentration increases the rate of reaction—more substrates are available to bind to the enzyme.
  • However, the rate will eventually plateau when all the enzyme's active sites are occupied (saturation point).

  When the enzyme is in excess, increasing substrate concentration allows more enzyme substrate complexes form.

  If the enzyme is limiting, then all of the active sites eventually become occupied.

  
• Elaborate inhibition

  Inhibitors reduce enzyme activity and can be either competitive or non-competitive.

  A competitive inhibitor is an inhibitor that has a similar shape to the substrate and so binds to the active site of an enzyme.

  Non-competitive inhibitors don’t bind to an enzyme’s active site: they bind to another part of the enzyme instead. They can bind to the enzyme even if the substrate is already at the active site.They cause the active site to change shape. This prevents enzyme-substrate complexes from forming.
• Why can non inhibitors become a problem?

  Since non-competitive inhibitors are effective even when the substrate is already at the active site, adding excess substrate does not overcome their effect.
• Elaborate temperature

  Increasing temperature gives molecules more kinetic energy, leading to more successful collisions between enzyme and substrate.

  After the optimum temperature, increasing the temperature further causes hydrogen bonds in the enzyme to break. 

   

  This changes the enzyme's tertiary structure. 

   

  When this happens, we say that the enzyme is denatured. 

   

  As more enzymes denature, the rate of reaction decreases. 
• what is pH a measure of?

  The pH of a solution is a measure of its H+ concentration.

   

  The higher the concentration of H+ ions, the lower the pH of the solution. 
• elaborate pH

  A change in pH breaks both the hydrogen and ionic bonds in an enzyme. 

   

  This changes the enzyme's tertiary structure. 

   

  When this happens, we say that the enzyme is denatured. 
• Effect of Temperature on Enzyme Activity graph


  Bell-shaped curve peaking at optimum temperature.

  
• Effect of pH on Enzyme Activity:

  Symmetrical bell curve centered around the optimum pH.

  
• Effect of Substrate Concentration on Rate:

  Increases rapidly, then plateaus when enzymes are saturated.

  
• Effect of Enzyme Inhibitors:

  • Competitive inhibitors increase the apparent Km (takes more substrate to reach the same rate).
  • Non-competitive inhibitors lower the maximum rate (Vmax) since they change the enzyme’s shape.