2.1.4 Enzymes

• Enzymes are biological catalysts which speed up metabolic reactions in living organisms without being used up
• Enzymes affect both the structure and function of the cell.
• What do enzymes do?

  Provide an alternative reaction pathway with lower activation energy needed for the reaction
• What is turnover number?

  The number of reactions an enzyme molecule can catalyse per second
• Intracellular reactions occur inside the cell
• Extracellular reactions occur outside the cell
• Enzymes must be secreted outside of the cell to catalyse extracellular reactions
• Intracellular enzymes could be part of a metabolic pathway
• Give an example of an intracellular enzyme

  Catalase
• Give two examples of extracellular enzymes

  Amylase

  Trypsin
• What is the role of catalase?

  To break down hydrogen peroxide into water and oxygen.
• What is hydrogen peroxide?

  A potentially harmful by-product of many metabolic reactions
• What is the fastest acting enzyme?

  Catalase
• What is the role of amylase?

  Breaks down starch into maltose
• Where is amylase made?

  Salivary glands and pancreas.
• Where does amylase act?

  Mouth and small intestine
• What is the role of trypsin?

  Digests proteins into smaller peptides
• Where is trypsin made?

  Pancreas
• Where does trypsin act?

  Small intestine
• Enzymes are globular proteins
• What is the active site of an enzyme?

  An indented area on the surface of an enzyme molecule, with a shape that is complementary to the shape of the substrate molecule
• How is the specific active site shape of an enzyme determined?

  The tertiary structure of the enzyme.
• What determines which substrate binds to an enzyme?

  R groups
• What is the specificity of an enzyme?

  Its ability to catalyse one type of reaction
• The specificity of an enzyme is a result of the complementary nature between the shape of the active site on the enzyme and its substrate(s)
• How is the shape of the active site determined?

  Tertiary structure of the protein
• What is the lock and key hypothesis?

  The substrate fits exactly into the enzymes active site
• What is the induced fit hypothesis?

  It suggests that the substrate interferes with bonds in the active site of an enzyme causing it to undergo a conformational change allowing the substrate to fit. This change in shape affects the substrate bonds and therefore lowers activation energy.
• What is an anabolic reaction?

  Smaller molecules -> large molecule
• What is a catabolic reaction?

  Large molecule -> smaller molecules
• Effect of increasing temperature on enzyme activity:

  1. Molecules gain kinetic energy
  2. Move faster
  3. More enzyme-substrate complexes form
  4. After optimum temperature enzyme starts to denature
• What is the optimum temperature of an enzyme?

  Temperature at which an enzyme catalyses at its maximum rate
• Why do enzymes denature at too high temperatures?

  Enzymes vibrate more, breaking bonds in the tertiary structure which permanently damages the active site preventing the binding of a substrate. It is denatured
• What does it mean for an enzyme to be denatured?

  It can no longer function
• Temperature coefficient (Q10) = Rate of reaction at ( T+10 ) °C / Rate of reaction at T °C
• The effect of pH on enzymes:

  1. Hydrogen ions and ionic bonds hold enzyme tertiary structure in place
  2. Outside of the optimum pH, excess hydrogen ions or hydroxide ions interfere with these bonds causing them to break
  3. This alters the shape of the active site
• What is a buffer?

  A solution that keeps the pH stable by donating or accepting hydrogen ions
• Why does pepsin have a low optimum pH?

  It is found in the acidic stomach environment
• Effect of increased enzyme concentration:

  1. More active sites available
  2. More successful collisions
  3. More enzyme-substrate complexes form
  4. Maximum rate of reaction is reached when substrate concentration becomes the limiting factor
• Effect of increased substrate concentration:

  1. More enzyme-substrate complexes form
  2. All active sites become saturated
  3. Enzyme concentration is now the limiting factor