Many Proteins are Enzymes

• How do enzymes act as biological catalysts?

  • Lowers the activation energy of each reaction it catalyses
  • To speed up reaction
• Describe the induced fit model of enzyme action

  1. Substrate binds to (not completely complementary) active site of enzyme
  2. Causing active site to mould around substrate so it is completely complementary
  3. Enzyme-Substrate Complex forms
  4. Causing bonds in substrate to bend/distort, lowering activation energy
• Explain the Specificity of Enzymes

  • Specific tertiary structure determines shape of active site (Dependent on primary structure)
  • Active site is complementary to a specific substrate
  • Only this substrate can bind to active site, inducing fit and forming an enzyme-substrate complex
• Describe and explain the effect of enzyme concentration on the rate of enzyme-controlled reactions

  As enzyme conc increases, rate of reaction increases

  • Enzyme conc = limiting factor (Excess substrate)
  • More enzymes = more available active sites
  • So more E-S complexes form

  At a certain n point, rate of reaction levels off

  • Substrate conc = Limiting factor (All substrates in use)
• Describe and explain the effect of substrate concentration on the rate of enzyme-controlled reactions

  A substrate conc increases, rate of reaction increases

  • Substrate conc = Limiting factor (Too few enzyme molecules to occupy all active sites)
  • More E-S complexes form

  At a certain point, rate of reaction levels off

  • Enzyme conc = Limiting factor
  • All active sites are saturated
• Describe and explain the effect of temperature on the rate of enzyme-controlled reaction

  As temp increases up to optimum, rate of reaction increases

  • More kinetic energy
  • More E-S complexes form

  As temp increases above optimum, rate of reaction decreases

  • Enzymes denature - Tertiary structure and active site change shape
  • As hydrogen/ionic bonds break
  • So active site is no longer complementary
  • So fewer E-S complexes form
• Describe and explain the effect of PH on the rate of enzyme-controlled reactions

  As PH increases/decreases above/below an optimum, rate of reaction decreases

  • Enzymes denature - tertiary structure and active site change shape
  • As hydrogen/ionic bonds break
  • So active site is no longer complementary
  • So fewer E-S complexes form
• Describe and explain the effect of concentration of competitive inhibitors on the rate of enzyme controlled reactions

  As conc of competitive inhibitors increases, the rate of reaction decreases

  • Similar shape to substrate
  • Competes for/binds to/blocks active site
  • So substrate can't bind and fewer E-S complexes form

  Increasing substrate conc reduces effect of inhibitors
• Describe and explain the effect of concentration of non-competitive inhibitors on the rate of enzyme-controlled reactions

  As concentration of non-competitive inhibitor increases, rate of reaction decreases

  • Binds to allosteric site
  • Changes enzyme tertiary structure/active site shape
  • So active site is no longer complementary to substrate
  • So substrates can't bind so fewer E-S complexes form

  Increasing substrate conc has no effect on rate of reaction as change to active site is permeant