3.4.1.2 - Enzymes

• What is the structure of enzymes?

  • Enzymes have a 'dent' in their structure known as the active site, which is specific and unique in its shape=> specific folding and bonding in the tertiary structure
  • Together they form an enzyme-substrate complex
  • Enzyme's shape is determined by the primary structure
• What is enzyme action?


  The certain amount of energy a reaction requires before they can occur
• What factors affect the rate of enzyme controlled environments?

  • Temperature
  • pH
  • Substrate concentration
  • Enzyme concentration
  • Inhibitors
• How does temperature effect enzyme action?


  As the temperature increases so does the kinetic energy which leads to more frequent collisions and therefore enzyme substrate complexes are formed rapidly

  • Low temperature => not enough kinetic energy for successful collisions between enzyme and substrate
  • High temperature => Weak bonds ( H bonds in tertiary structure) break and change active site's shape, so enzyme denatures and enzyme-substrate complexes can't form
• How does enzyme concentration effect enzyme action?


  As the substrate concentration increases so does the rate of reaction until it eventually plateaus and stops increasing as they're is an increase in the number of successful collisions between the enzyme and the substrate

  • plateaus because eventually all active sites are occupied/saturated so the rate of reaction is at its maximum
• What is a competitive inhibitor?

  A molecule that is the same shape as the substrate and can bind to the active site
• How does a competitive inhibitor effect enzyme action?


  They bind to the active site and prevent the substrate from binding and the reaction occurring
• How does a low substrate concentration effect enzyme action?


  There is a higher chance of an inhibitor molecule colliding with the active site which therefore lowers the rate of reaction
• How does a high substrate concentration effect enzyme action?

  There is a higher chance of a substrate molecule colliding with the active site rather than the inhibitor, knocking them out of the active site and therefore increasing the rate of reaction
• What is the lock and key hypothesis?

  A model that shows the substrate is complementary to the active site and they bind together to form an enzyme-substrate complex as it reduces the activation energy and allows the reaction to occur
• What is a strength of the lock and key hypothesis?


  It explains enzyme specificity
• What is a weakness of the lock and key hypothesis?


  It doesn't explain that some enzymes work on a small number of similar substrates
• What is the induced fit theory?


  A model that explains that the substrate and enzyme interact with each other and the active site changes shape slightly, which distorts the substrate and causes bonds to break and reform in the substrate- reducing the activation energy required
• What are the strengths of the induced fit theory?

  • Explains how the enzyme-substrate complex lowers the activation energy
  • Explains how products are released as the active site is complementary to the transition state not the products
  • Flexibility of the active site explains how an enzyme may act on 2 similar but not identical substrates
  • Flexibility of the proteins also provides a better explanation of non-competitive inhibitors