CR more notes

• Glucose broken down

  1. Removal of hydrogen ions and electrons by dehydrogenase enzymes

  2. Release of ATP
• Metabolic pathways of cellular respiration

  • Central to metabolism
  • Yield energy
  • Connected to many other pathways
• Role of ATP

  • Transfer of energy
  • Phosphorylation of molecules
• ATP


  Used to transfer energy to synthetic pathways and other cellular processes where energy is required
• Metabolic pathways of cellular respiration

  1. Breakdown of glucose to pyruvate in the cytoplasm in glycolysis

  2. Progression pathways in the presence or absence of oxygen (fermentation)
• Glycolysis

  1. Phosphorylation of intermediates in an energy investment phase

  2. Direct generation of ATP in an energy pay-off stage

  3. Role of the enzyme phosphofructokinase
• First phosphorylation


  Leads to a product that can continue to a number of pathways
• Second phosphorylation, catalysed by phosphofructokinase

  Irreversible reaction leading only to the glycolytic pathway
• Pyruvate

  Progresses to the citric acid cycle if oxygen is available
• Formation of citrate

  1. Pyruvate is broken down to an acetyl group

  2. Acetyl group combines with coenzyme A to be transferred to the citric acid cycle as acetyl coenzyme A

  3. Acetyl (coenzyme A) combines with oxaloacetate to form citrate

  4. Enzyme mediated steps of the cycle

  5. Cycle results in the generation of ATP, the release of carbon dioxide and the regeneration of oxaloacetate in the matrix of the mitochondria
• Dehydrogenase enzymes


  1. Remove hydrogen ions and electrons

  2. Passed to the coenzymes NAD or FAD to form NADH or FADH2 in glycolysis and citric acid pathways

  3. NADH and FADH2 release the high-energy electrons to the electron transport chain on the mitochondrial membrane

  4. Results in the synthesis of the bulk of the ATP
• Electron transport chain

  • Collection of proteins attached to a membrane
  • NADH and FADH2 release the high-energy electrons to the electron transport chain where they pass along the chain, releasing energy
  • Energy used to pump H ions across the inner mitochondrial membrane
  • Return flow of H ions drives ATP synthase and produces the bulk of the ATP generated by cellular respiration
• ATP synthesis

  1. High energy electrons are used to pump hydrogen ions across a membrane

  2. Flow of these ions back through the membrane synthesises ATP using the membrane protein ATP synthase
• Return flow of these ions


  Rotates part of the membrane protein ATP synthase, catalysing the synthesis of ATP
• The final electron acceptor is oxygen, which combines with hydrogen ions and electrons to form water
• Substrates for respiration

  • Starch
  • Glycogen
  • Other sugar molecules
  • Amino acids
  • Fats
• Starch and glycogen


  Broken down to glucose for use as a respiratory substrate
• Other sugar molecules

  Can be converted to glucose or glycolysis intermediates for use as respiratory substrates
• Proteins

  Can be broken down to amino acids and converted to intermediates of glycolysis and the citric acid cycle for use as respiratory substrates
• Fats


  Can be broken down to intermediates of glycolysis and the citric acid cycle
• Regulation of the pathways of cellular respiration


  1. By feedback inhibition

  2. Regulation of ATP production, by inhibition of phosphofructokinase by ATP and citrate

  3. Synchronisation of rates of glycolysis and citric acid cycle
• Cell conserves its resources

  Only producing ATP when required
• ATP supply increases

  With increasing rates of glycolysis and the citric acid cycle
• ATP supply decreases

  When glycolysis and citric acid cycle pathways slow down
• If the cell produces more ATP than it needs


  ATP inhibits the action of phosphofructokinase slowing the rate of glycolysis
• Rates of glycolysis and the citric acid cycle are synchronised

  By the inhibition of phosphofructokinase by citrate
• If citrate accumulates

  Glycolysis slows down
• When citrate consumption increases

  Glycolysis increases the supply of acetyl groups to the citric acid cycle