Enzymes

• Enzymes


  Biological catalysts that increase the rate of reactions
• Amylase


  Catalyzes the breakdown of starch molecules into the disaccharide maltose
• Substrate


  The molecule that the enzyme attaches to
• Products


  The molecules that are produced by the enzyme-catalyzed reaction
• Enzyme-substrate complex


  When the substrate molecule fits perfectly into the active site of the enzyme
• Enzyme present


  Activation energy barrier is lower than without the enzyme
• Lock and key model

  The tertiary structure of the active site is fixed and does not change shape, the substrate molecule slots perfectly into the active site
• Effective temperature on enzymes

  The effect of temperature on the rate of enzyme-controlled reactions
• Investigating the effect of temperature on enzyme-controlled reactions

  1. Select an enzyme

  2. Measure amount of product formed over time

  3. Repeat at range of temperatures

  4. Draw tangents to measure rate at each temperature

  5. Ensure tangents drawn at same time point
• Effect of temperature on enzyme-controlled reactions

  • Rate increases as temperature increases up to optimum temperature
  • Rate decreases as temperature increases past optimum temperature
• Increasing temperature


  • Increases kinetic energy of enzyme and substrate
  • Increases frequency of collisions between substrate and active site
  • Increases rate of reaction
• Optimum temperature


  Temperature at which reaction rate is maximum
• Human enzymes have optimum temperature around 40°C
• Enzymes in organisms like bacteria in hot springs have optimum temperature around 70-80°C
• Effect of temperature above optimum

  1. Enzyme molecules vibrate more rapidly

  2. Bonds within enzyme break

  3. Tertiary structure changes

  4. Active site no longer complementary to substrate

  5. Enzyme denatures and no longer functions
• Denatured enzymes cannot renature if cooled back down
• pH


  Measure of the concentration of hydrogen ions in a solution
• Low pH (e.g. pH 2)


  High concentration of hydrogen ions
• High pH (e.g. pH 6)


  Low concentration of hydrogen ions
• Enzymes


  • Affected by pH
  • Work fastest at a specific optimum pH
• Enzymes with different optimum pH

  • Salivary amylase (optimum pH around 7)
  • Enzyme in stomach (optimum pH around 2)
• pH changes away from optimum pH

  Rate of enzyme reaction decreases
• How pH affects enzymes

  1. Hydrogen ions can bond with R groups of amino acids in active site

  2. Hydrogen ions can break bonds holding tertiary structure in place
• pH falls (concentration of hydrogen ions rises)


  Bonds between amino acids break
• pH rises (concentration of hydrogen ions falls)


  Bonds between amino acids form
• Significant pH change


  Active site changes shape so much that it's no longer complementary to substrate, enzyme denatures
• Steps to calculate pH

  1. Enter [H+] into calculator

  2. Press log button

  3. Reverse sign to get pH
• Frequency of collisions


  The number of collisions per second between the substrate molecules and the active site of the enzyme
• Substrate concentration is doubled


  Frequency of collisions between substrate and active site also doubles
• Frequency of collisions between substrate and active site doubles


  Rate of reaction also doubles
• Rate of an enzyme catalyzed reaction

  • Directly proportional to the substrate concentration
• V max


  The fastest rate at which the enzyme can work
• Enzyme is saturated


  Every active site is colliding with a substrate molecule, so increasing substrate concentration further will not increase the rate
• Enzyme concentration is low, substrate concentration is high


  Rate of reaction is relatively low
• Enzyme concentration is doubled


  Frequency of collisions between substrate and active sites also doubles
• Rate of an enzyme catalyzed reaction

  • Directly proportional to the enzyme concentration, provided there is more substrate than enzyme
• If the amount of substrate becomes limited, increasing the enzyme concentration further will not increase the rate