UNIT 2 - Enzymes in metabolic pathways

• Metabolism

  Integrated and controlled pathways of enzyme catalysed reactions within a cell
• Metabolic Pathway

  1. Reversible - Reactant can be converted into a product and the product can be converted back into the reactant

  2. Irreversible - The reactant can only be converted into the product

  3. Alternative Route - Allows steps in the pathway to be bypassed
• Types of Metabolic Reactions

  • Catabolic reaction (Energy Release) - Breakdown of large complex molecule into smaller ones
  • Anabolic Reaction (Energy Required) - Biosynthesis of complex molecules from simpler ones
• Phospholipids


  Create fluidity in membrane
• Role of Proteins


  • Pumps - pumps ions into or out of the cell by active transport (Low to high concentration & requires ATP)
  • Pores - moves molecules into or out of the cell by diffusion (high to low concentration & no ATP required)
  • Enzymes - Biological catalyst found in the cell membrane
• Induced Fit Theory


  When the active site changes shape to better fit the substrate after the substrate has bound
• Enzyme Action - Induced Fit


  1. Substrate has a high affinity for the active site

  2. The shape of the active site ensures correct orientation of the reactants

  3. Chemical bonds in the substrate weaken lowering activation energy

  4. Products are released as they have a low affinity for the active site
• Activation Energy


  The energy required to break chemical bonds in the reactant molecules to speed up reactions
• Enzymes speed up reactions as they lower the activation energy required to form products from the reactants
• Controlling metabolic pathways


  1. To control metabolic pathways, control of enzymes are required

  2. Each enzyme in the pathway is controlled by a specific gene which can be switched on or off

  3. This saves energy
• Factors affecting enzyme activity


  • PH
  • Temperature
  • Substrate concentration
  • Product concentration
• Increased substrate concentration (A)

  Promotes forward reaction
• Increased product concentration (B)

  Promotes backwards reaction
• Substrate Concentration Graph

  • As the substrate concentration increases, the enzyme activity increases until the substrate is no longer the limiting factor
• Low substrate concentration - Not enough substrates to fit into all the available active sites
• Higher substrate concentration - Lots of substrates available to fit into the enzyme's active sites
• Very high substrate concentration - All active sites filled. Adding more substrate has no effect because there are no more available active sites
• Types of Enzyme Inhibition


  • Competitive
  • Non-competitive
  • Feedback Inhibition
• Competitive Inhibitors


  • Inhibitor molecule binds to the active site of the enzyme, preventing the substrate from binding
  • The competitive inhibitors resembles the substrate
  • Competitive inhibition can be reversed by increasing substrate concentration
• Non-competitive Inhibitors


  • Inhibitor molecule binds away from the active site but changes its shape preventing the substrate from binding
  • Non-competitive Inhibition cannot be reversed by increasing substrate concentration
• Feedback Inhibition


  • When the end product in a pathway reaches a critical concentration, the end product inhibits the first enzyme in a pathway
  • This prevents further synthesis of the end product, this saves energy