metabolic pathways 1

• Metabolic pathways

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

  • Can have reversible, irreversible and alternative routes
  • Reactions are either anabolic or catabolic
• Anabolic reactions

  Involve the building up of large molecules from small molecules and require energy
• Catabolic reactions

  Breakdown large molecules into smaller molecules and release energy
• Proteins in the membrane

  • Pores (allowing molecules to pass through)
  • Pumps (allowing molecules to pass through the membrane, however this requires energy – so the molecule is actively pumped inside or outside of the cell)
  • Enzymes (catalysing chemical reactions)
• Metabolic pathways

  Are controlled by the presence or absence of key enzymes
• Factors that control the rate of enzyme activity

  Temperature and pH, will also regulate the rate of a metabolic pathway
• Induced fit

  When a substrate binds to the active site, the active site will change shape to better fit the substrate
• Activation energy

  Energy required to start a chemical reaction, can be overcome by heating or adding a catalyst
• Enzymes

  Biological catalysts that lower the activation energy required for a reaction
• Substrate affinity

  Substrate molecules have high affinity for the active site which allows them to bind easily
• Product affinity

  Product molecules have a low affinity for the active site and this allows them to leave the active site
• Reversible metabolic pathways

  • The presence of a substrate or the removal of a product will drive a sequence of reactions in a particular direction
• Competitive inhibitors

  Bind at the active site preventing the substrate from binding, 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, cannot be reversed by increasing substrate concentration
• Feedback inhibition

  Occurs when the end-product in the metabolic pathway reaches critical concentration, the end-product inhibits an earlier enzyme, blocking the pathway, and so prevents further synthesis of the end product