Model of Action

• What are enzymes classified as?

  Biological catalysts
• What type of proteins are enzymes?

  Globular proteins
• Why are enzymes called biological catalysts?

  They increase reaction rates without being used up
• What do enzymes do to the activation energy of a reaction?

  They lower the activation energy
• What is activation energy?

  The energy required to start a reaction
• How do enzymes affect the temperature at which reactions occur?

  They allow reactions at lower temperatures
• What are the two categories of enzymes?

  • Intracellular enzymes
  • Extracellular enzymes
• Where do intracellular enzymes act?

  Within the cells that produce them
• What does catalase do?

  Breaks down hydrogen peroxide into water and oxygen
• Where do extracellular enzymes act?

  Outside the cells that produce them
• What does amylase do?

  Breaks down starch into maltose
• What does trypsin do?

  Breaks down proteins into smaller polypeptides
• What are the two models explaining enzyme action?

  • Lock and key hypothesis
  • Induced-fit model
• What does the lock and key model suggest?

  The substrate fits perfectly into the active site
• How does the induced-fit model differ from the lock and key model?

  The substrate does not fit perfectly initially
• What happens to the active site in the induced-fit model?

  It changes shape slightly as the substrate enters
• What effect does the induced-fit model have on the substrate's bonds?

  It puts a strain on the substrate's bonds
• How does the induced-fit model affect activation energy?

  It lowers the activation energy
• How do enzymes work?

  • An enzyme's active site is complementary to a substrate
  • Substrate binds to active site forming an enzyme-substrate complex
  • Bonds form between R groups within active site & substrate
  • Substrate is broken down into products
• How do an enzyme & substrate react?

  The substrate & active site must collide with each other at the correct speed & orientation