B1- Metabolism and Survival

• Metabolic pathways consist of several stages involving the conversion of one metabolite to another
• Each step is controlled by a particular enzyme.

  Each enzyme is coded by a particular gene.
• Reactions can be called either anabolic or catabolic.
• Anabolic- Synthesis

  Catabolic- Degredation
• Anabolic requires energy, catabolic releases energy
• Enzymes have a specific shape, their active site is shaped to fit their specific substrate and are said to be complementary
• An enzyme and substrate are said to have high affinity for each other before combining at the active side to produce a substrate or product
• Induced fit model is when the active site changed shape to better fit the substrate after it binds
• Products of the reaction have low affinity for the active site and are released
• Activation energy is the energy required to initiate a reaction. The substrate must overcome the barrier to change into a product
• 5 factors which can affect the rate at which an enzyme works at:

  • Temperature,
  • pH,
  • Enzyme concentration,
  • Substrate concentration,
  • End product concentration
• Feedback inhibition occurs when the end product reaches a critical concentration.
• Inhibitors are substances which prevent enzyme activity
• Competitive inhibitors compete with the substrate to fit into the active site. Similar structure, reaction rate is reduced if the inhibitor blocks the active site
• If the concentration of substrate is low then the inhibitors will win over the active site reducing reaction rate.

  If the concentration of substrate is high the substrates will win over the active site increasing reaction rate to its optimum
• Non competitive inhibitors will bind elsewhere on the enzyme (allosteric site) causing active site to change shape and prevents the substrate from binding.