CONCEPT 9/10. Cellular Respiration

• Where does glycolysis take place?

  Cytosol
• Where does pyruvate oxidation take place?

  Mitochondrial matrix
• Where does the TCA cycle take place?

  Mitochondrial matrix
• Where does oxidative phosphorylation take place?

  Mitochondrial inner membrane
• What occurs in glycolysis?

  Glucose (6C) is broken down into two molecules of pyruvate (3C), producing 2ATP, 2NADH and 2H20. Occurring over 10 steps, step 1-5 is known as the energy investment phase (endergonic) and requires 2 ATP whilst 6-10 is known as the energy payoff phase and is exergonic, producing 4 ATP.
• How is glycolysis regulated?

  Mainly occurs in step 3. If high levels of ATP, phospho-fructokinase will be inhibited which is responsible for phosphorylating fructo 6-phosphate into fructose 1,6-biphosphate. As a result, the steps of glycolysis is unable to proceed
• How can a cell generate energy when oxygen is absent?

  If there is a lack of oxygen, anaerobic respiration will follow glycolysis in place of aerobic respiration.
• If anaerobic respiration doesn't produce ATP, why is it beneficial?

  Anaerobic respiration allows glycolysis to continue as it oxidises NADH back to NAD+ which is required for glycolysis. Glycolysis is capable of generating 2 ATP molecules and thus if this process continues, a cell is still able to produce energy.
• What are the products of alcoholic fermentation?

  The products of alcoholic fermentation are ethanol and carbon dioxide.
• What are the products of lactic acid fermentation?

  Lactate
• What enzymes are involved in alcoholic fermentation?

  Pyruvate decarboxylase and alcohol dehydrogenase
• What enzymes are involved in lactic acid fermentation?

  Lactate dehydrogenase
• What occurs in pyruvate oxidation?

  • Pyruvate enters the mitochondria via. porins/mitochondrial pyruvate carriers and binds to a pyruvate dehydrogenase complex
  • A carboxyl group is removed, releasing CO2
  • The two carbon molecule is oxidised to become an acetyl-group
  • The released electrons reduce NAD+ to NADH
  • The acetyl-group is transferred to CoA to form acetyl CoA
• Inputs and outputs of pyruvate oxidation?

  Inputs: Pyruvate and NAD+

  Outputs: CO2 and Acetyl CoA
• What occurs during the Krebs cycle?

  • Acetyl-CoA (2C) binds with oxaloacetate (4C) to form citrate (6C)
  • Citrate undergoes two decarboxylation reactions, releasing 2CO2 and giving rise to succinyl-CoA (4C)
  • Succinyl-CoA is (4C) is converted to oxaloacetate, ready to bind to acetyl-CoA and continue the cycle
• What are the inputs of the citric acid cycle?

  Acetyl-CoA, 3NAD+, 1FAD+, GPD+Pi, H20
• What are the outputs of the citric acid cycle?

  2CO2, 3 NADH, GTP, FADH2
• What occurs in oxidative phosphorylation?

  • Electrons carried by NADH and FADH2 from glycolysis and the citric acid cycle provide electrons to the electron carriers of the inner mitochondrial membrane. As the electrons travel through an electron transport chain, protons will be transferred out of the matrix and into the intermembrane space.
  • Once the electron leaves the last protein complex, oxygen is reduced and H20 is formed
  • ATP synthase utilises the proton gradient created and moves protons down its concentration gradient, back into the matrix, obtaining the energy needed to form ATP.
• Why must oxygen be present in oxidative phosphorylation?

  If there is no oxygen present, the electrons will not pass through the electron transport chain as oxygen serves as its final acceptor. Therefore, NADH and FADH2 will not be converted into NAD+ and FAD for use in the TCA cycle, inhibiting both processes.