chapter 4

• Why are enzymes important?

  They are biological catalysts necessary for reactions vital for life
• What type of protein are enzymes?

  Enzymes are globular proteins
• What are anabolic reactions?

  Making larger molecules from smaller nodes, will form organelles, cells, tissues, organs and organ systems
• What are catabolic reactions?

  Reactions which involve breaking down larger molecules to smaller ones, for example digestion
• What is meant by Vmax in relation to enzymes?


  Enzymes can also increase the rate of reaction to its max- Vmax
• What is the active site?

  An area within the tertiary structure of an enzyme which has a shape complementary to a specific substrate molecule
• What is the lock and key hypothesis?

  Suggests that only a specific substrate will fit the active site of an enzyme.
• What is an enzyme-substrate complex?

  When the substrate is bound to the active site.
• What is an enzyme-product complex?

  When the substrate has reacted and the product forms, forming an enzyme-product complex
• What is the induced fit hypothesis?

  The induced fit model suggest that when a substrate binds to an enzyme’s active site, it causes the active site to change shape as well.
• What are intracellular enzymes?


  Enzymes which act within a cell
• How is the enzyme catalase a useful intracellular enzyme?

  Hydrogen peroxide is a toxic product of many metabolic pathways

  • Catalase breaks it down to form water and oxygen
  • Prevents accumulation
• Why are extracellular reactions necessary?

  They are necessary to break down nutrients so that they are smaller components able to enter through the cell-surface membrane
• What are examples of extracellular enzymes?

  Digestion of protein- PROTEASES break down proteins into smaller peptides then amino acids

  Digestion of starch- AMYLASE breaks down starch to maltose, MALTASE breaks down maltose to glucose
• What factors affect enzyme activity?

  • Temperature
  • pH
  • Substrate Concentration
  • Enzyme Concentration
• How does temperature increase enzyme activity?

  • Increases the kinetic energy of the particles
  • Therefore they move faster and collide more frequently
  • Leads to more successful collisions between substrate and enzyme, increasing rate of reaction
• What happens if the temperature goes above optimum temperature?

  • Denaturation of enzymes
  • Vibrations increase too much, breaking the bonds and changing the tertiary structure of the protein
  • Active Site of the enzyme no longer complementary to substrate, therefore enzyme has denatured and no longer functions
• What is the optimum temperature?

  The temperature at which the enzyme has the highest rate of activity
• What is the average optimum temperature in the human body?

  40 degrees celsius
• What is the temperature coefficient?

  Q10, a measure of how much the rate of reaction with a 10ºC rise in temperature
• What are thermophiles?


  Organisms adapted to living in very hot environments; the enzymes present in these organisms are more stable than others due to the increased number of bonds therefore their active sites are more resistant to change as the temp rises
• How does pH affect enzyme activity?

  • Hydrogen and ionic bonds hold together the tertiary structure of the enzyme
  • If the solution is too acidic or too alkaline, these bonds can break resulting in the active site changing shape
  • Therefore the enzyme is denatures
• What happens if the pH returns to the optimum?

  The protein will resume its natural state; called renaturation
• How does substrate/enzyme concentration affect enzyme activity?

  An increase in concentration leads to more successful collisions and an increase in reactions to its Vmax
• What are inhibitors?


  Molecules that prevent enzymes carrying out catalysis
• What are competitive inhibitors?

  • They have a similar shape to the substrate
  • The bind to the active site of the enzyme so the substrate cant
  • Substrate and Inhibitor "compete" to bind to the active sites
• What is an example of a competitive inhibitor?

  • Statins
  • Aspirin
• What is non-competitive inhibition?

  • The inhibitor binds to an alternative site called the allosteric site
  • This changes the tertiary structure of the enzyme
  • Changes the shape of the active site; no longer complementary to the substrate and is unable to bind together
• What is end product inhibition?

  When the product of a reaction acts as an inhibitor to the enzyme that produces it- serves as negative feedback.
• What are cofactors?


  Cofactors are non-protein molecules that assist enzymes in carrying out their catalytic functions.
• What is a coenzyme

  An organic cofactor
• What are inorganic cofactors?

  Obtains via diet as minerals, e.g. calcium, zinc, iron and chloride ions

  • enzyme amylase contains a chloride ion which is necessary for the formation of a correctly shaped active site
• How are coenzymes formed?

  Derived from vitamins, a class of organic molecules found in the diet

  • e.g. vitamin B5, needed to make coenzyme A
• What are prosthetic groups?

  Cofactors tightly bound to and form permanent feature of the enzyme protein.
• What are inactive precursor enzymes?


  Enzymes produced in an inactive form.
• How do you activate a precursor enzyme?

  By addition of a cofactor, which changes the tertiary structure to make the active site complementary to the substrate.
• What is the precursor enzyme called before, and after, activation?

  • A apoenzyme
  • Turns into a holoenzyne (active)
• What is it called when a change in conditions activates a precursor enzyme instead?

  zymogens or proenzymes