Cellular respiration

• INNER MEMBRANE divides the MATRIX from the INTERMEMBRANE SPACE
• NADH donates its pair of electrons toComplex I

  • This oxidizes NADH back to NAD+ (oxidation)
• FADH 2 donates its pair of electrons to Complex II

  • This oxidizes FADH 2 back to FAD+ (oxidation)
• Within each enzyme, electrons get transferred along a series of electron acceptors and donors (“redox centers”)
• Each transfer (redox rx) releases ENERGY within the enzyme

  • Generating a flow of electrons thru each enzyme, creating “electrical current”
• Complex I can use this energy to actively pump protons (H +) from the matrix into intermembrane space = electrochemical gradient!

  • Complex II helps pump protons indirectly
• INTERMEMBRANE SPACE starts to become more positive and more physically concentrated with protons compared to MATRIX
• Protons (H +) will want to go down back to matrix to reach equilibrium ...but they can’t!
• Once electrons in Complex I and Complex II have transferred through series acceptors /donors, their work isn’t done
• Electrons get transferred to a NEW type of electron carrier, Coenzyme Q, which gets reduced to CoQH2
• Coenzyme QH 2 transports electrons to Complex III where they undergo more energy-releasing transfers to power H + pump
• Finally, electrons are loaded onto another new carrier, Cytochrome C 3+ , and transferred to Complex IV where they undergo more energy-releasing transfers to power H + pumps
• In Complex IV, O 2 acts as the final electron receptor, producing 2 H2O molecules as the final product
• The # of ATPs produced by ATP synthase is proportional to the number of protons pumped across inner membrane
• Chemiosmosis: ATP synthase uses energy from the passive flow of protons (H + ) down their electrochemical gradient from the INTERMEMBRANE SPACE back into MATRIX to power synthesis of ATP
• A channel in ATP synthase on INTERMEMBRANE SPACE side allows protons (H + ) to flow into MATRIX, towards equilibrium

  • [Transforms electrochemical gradient’s potential energy into kinetic energy]
  • Turns “rotor”
• Rotational (kinetic) energy from rotor powers other parts of enzyme on MATRIX side to form bonds between: ADP and ATP
• 1 proton ~ 1 rotation ~ 3 ATP molecule
• Electron Transport chain

  1. Harness potential energy from electrons
  2. Use it to pump protons across membrane
  3. Generate electrochemical gradient
  4. (Chemiosmosis) -> Release potential energy to power molecular rotor
  5. Use rotational energy to catalyze ATP synthesis
• The goal of cellular respiration is to break down the food you eat and make ATP out of it