cellular respiration

• Cellular respiration


  The process by which cells convert the chemical energy in food molecules into a form that can be used by the cell
• What you need to know

  • Describe the movement of electrons and hydrogens during redox reactions
  • Explain the importance of coenzymes (NAD+ and FAD) during cellular respiration
  • Describe or draw the structure of a mitochondrion
  • Explain how metabolic pathways produce energy within cells
  • Describe the stages of aerobic respiration, including where they take place, when ATP and waste products are produced
  • Describe the route taken by the carbon atoms within a glucose molecule throughout the process of aerobic cellular respiration
  • Compare and contrast aerobic and anaerobic cellular respiration
• Cellular respiration


  Uses chemical (potential) energy in food (e.g. glucose - C6H12O6)
• Cellular respiration


  Glucose + Oxygen -> Carbon dioxide + Water + Energy
• Cellular respiration


  EXERGONIC REACTION, ΔG = -686kcal mole-1
• ATP production


  ATP -> ADP + P + Energy (7.3kcal mole-1)
• 1 molecule glucose -> 36 or 38 molecules ATP, 38-40% of free energy from glucose
• Redox reactions


  Electrons are transferred in chemical reactions, relocation of electrons releases energy stored in food molecules, which is used to make ATP
• Reduction


  Gain of an electron
• Oxidation


  Loss of an electron
• Redox reactions


  • Na + Cl -> Na+ + Cl-
  • C6H12O6 + 6O2 -> 6CO2 + 6H2O
• Oxidoreductases


  Enzymes that catalyse redox reactions
• Coenzymes


  Small organic molecules that help enzymes catalyse reactions, cannot catalyse reactions themselves
• NAD+


  Coenzyme involved in oxidation and reduction reactions, accepts 2 electrons + 1H+
• FAD


  Coenzyme involved in oxidation and reduction reactions, accepts 2 electrons and 2H+
• Aerobic respiration


  1. Glycolysis (in cytoplasm, no oxygen required, 2 ATP produced, 2 NADH produced)

  2. Transition/link/preparation reaction (in mitochondrial matrix, pyruvate oxidized to acetyl CoA, CO2 and NADH produced)

  3. Krebs cycle (in mitochondrial matrix, CO2, NADH and FADH2 produced, 2 ATP produced)

  4. Electron transport chain (in mitochondrial cristae, electrons passed along carriers, protons pumped into intermembrane space, ATP synthase uses proton gradient to produce ATP)
• Glycolysis produces 2 pyruvate, 2 NADH and 2 ATP
• Link reaction converts 2 pyruvate to 2 acetyl CoA, producing 2 CO2 and 2 NADH
• Krebs cycle produces 4 CO2, 6 NADH, 2 FADH2 and 2 ATP
• Electron transport chain uses NADH and FADH2 to produce 28-30 ATP
• Total ATP produced in aerobic respiration is 38-40 per glucose molecule
• Mitochondrion


  • Double membrane with intermembrane space, cristae are inner folds of membrane, matrix is innermost compartment filled with gel-like fluid, transition reaction and Krebs cycle enzymes in matrix, electron transport system in cristae, most ATP produced in mitochondria
• Anaerobic respiration (fermentation)


  1. Glycolysis produces 2 ATP, 2 NADH

  2. Alcoholic fermentation: Pyruvate -> Ethanol + CO2

  3. Lactic acid fermentation: Pyruvate -> Lactic acid
• Anaerobic respiration produces only 2 ATP per glucose, compared to 32-38 ATP in aerobic respiration
• Anaerobic respiration is only about 2% efficient compared to 39% for aerobic respiration
• Oxygen is crucial for efficient energy supply, driving evolution of complex organisms with good oxygen supply mechanisms
• Oxidative phosphorylation occurs during the electron transport chain.
• ATP synthase uses energy released by protons moving through it to synthesize ATP.
• The electron transport chain is the final step in aerobic respiration, where electrons are passed from one carrier to another.