Metabolic Pathways

    Cards (5)

    • Metabolic Pathways are Enzyme Catalysed Reactions.
      Metabolic Pathways can have :
      Reversible steps
      Irreversible steps
      Alternative steps
      Reactions within metabolic pathways can be :
      Anabolic reactions which build up large molecules from small molecules and require energy.
      Catabolic reactions which break down large molecules into smaller molecules and release energy.
    • Controlled by Presence/Absence of Enzymes
      Induced fit occurs when the active site changes shape to better fit the substrate after the substrate binds.
      When the substrate binds with the enzyme the activation energy for the reaction is reduced.
      The substrate molecule has a high affinity for the active site.
      The subsequent products have a low affinity allowing them to leave the active site.
    • Substrate Concentration on Enzymes 

      The rate of enzyme reactions can be affected by substrate concentration.
      As the substrate concentration increases the enzyme reaction increases until all of the active sites are occupied by the substrate.
      When all the active sites are occupied adding more substrate makes no difference to the reaction rate.
      Some metabolic reactions are reversible and the presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction.
    • Control of Metabolic Pathways
      Competitive inhibitors bind at the active site preventing the substrate from binding.
      Competitive inhibition can be reversed by increasing substrate concentration.
      Non-competitive inhibitors bind away from the active site but change the shape of the active site preventing the substrate from binding.
      Non-competitive inhibition cannot be reversed by increasing substrate concentration.
    • Feedback Inhibition
      Feedback inhibition occurs when the end-product in the metabolic pathway reaches a critical concentration.
      The end-product then inhibits an earlier enzyme, blocking the pathway and so prevent further synthesis of the end-product.