Electron Transport Chain and Oxidative Phosphorylation

• What is the essential question addressed in BTN223?


  How do cells oxidize NADH and FADH₂ to convert their reducing potential into ATP?
• What is the role of the citric acid cycle in energy production?


  • Oxidizes acetyl-CoA into CO₂
  • Captures electrons as NADH and FADH₂
  • Provides reducing potential for ATP production
• Where does the electron transport chain occur?


  In the inner membrane of the mitochondria
• What are the reduced coenzymes produced by catabolic pathways?


  NADH and FADH₂
• What is the final electron acceptor in the electron transport chain?


  Oxygen
• What is the process of oxidative phosphorylation?


  • Phosphorylation of ADP to form ATP
  • Driven by the proton gradient generated during electron transport
• What is the structure of mitochondria?


  Mitochondria have a simple outer membrane and a complex inner membrane with cristae.
• What is the function of the cristae in mitochondria?


  They provide a large surface area for electron transport proteins.
• How many protein complexes are involved in the electron transport chain?


  Four protein complexes
• What role does coenzyme Q play in the electron transport chain?


  It shuttles electrons between protein complexes.
• How do electrons flow through the electron transport chain?


  Electrons fall in energy from complexes I and II to complex IV.
• What happens to electrons as they pass through the electron transport chain?


  • Each compound is reduced by gaining electrons.
  • Electrons are oxidized by donating electrons to the next compound.
  • Free energy is generated as electrons become more stable.
• What is the role of oxygen in the electron transport chain?


  Oxygen acts as the final electron acceptor, forming water.
• What is the net reaction when NADH is oxidized?


  NADH → NAD⁺ + 2e^- + H⁺
• What is the function of ATP synthase in oxidative phosphorylation?


  • Protons move through ATP synthase from the intermembrane space to the matrix.
  • This movement drives the synthesis of ATP from ADP and inorganic phosphate.
• What are the four main complexes of the electron transport chain?


  Complex I, Complex II, Complex III, Complex IV
• What is the function of Complex I in the electron transport chain?


  It accepts electrons from NADH and transfers them to coenzyme Q.
• What is the role of Complex II in the electron transport chain?


  It links the citric acid cycle to the electron transport chain by transferring electrons from succinate to coenzyme Q.
• How does Complex III function in the electron transport chain?


  It transfers electrons from coenzyme Q to cytochrome c through the Q cycle.
• What is the function of Complex IV in the electron transport chain?


  It transfers electrons from cytochrome c to molecular oxygen, reducing it to water.
• What are the components of the electron transport chain?


  • Complex I: NADH-coenzyme Q reductase
  • Complex II: Succinate-coenzyme Q reductase
  • Complex III: Coenzyme Q reductase
  • Complex IV: Cytochrome c oxidase
  • Other components: Coenzyme Q, Cytochromes, Iron-Sulphur proteins, Copper Proteins
• What is the role of NADH in the electron transport chain?


  NADH donates electrons to Complex I.
• How does coenzyme Q function as an electron carrier?


  Coenzyme Q can accept or donate electrons one or two at a time.
• What are flavoproteins and their role in the electron transport chain?


  Flavoproteins contain FAD or FMN and can accept or donate electrons one or two at a time.
• What is the role of cytochromes in the electron transport chain?


  Cytochromes transfer one electron at a time using heme prosthetic groups.
• How do iron-sulphur proteins participate in the electron transport chain?


  They participate in one electron transfers involving Fe²⁺ and Fe³⁺ oxidation states.
• What is the overall process of the electron transport chain?


  1. Electrons from NADH and FADH₂ are transferred through complexes.
  2. Free energy generated is used to pump protons into the intermembrane space.
  3. Proton motive force drives ATP synthesis via ATP synthase.
  4. Oxygen is the final electron acceptor, forming water.
• What is the net reaction of succinate in Complex II?

  Succinate + CoQ → Fumarate + CoQH₂
• Why does Complex II not pump protons across the inner mitochondrial membrane?


  The free energy change of the overall reaction is too small.
• What is the flow of electrons through Complex I and II?


  • Complex I: NADH → FMN → Fe-S → CoQ
  • Complex II: Succinate → FADH₂ → Fe-S → CoQ
  • Both complexes transfer electrons to Coenzyme Q.
• What is the significance of the proton motive force generated during electron transport?


  It drives the synthesis of ATP through ATP synthase.
• What is the role of the Q cycle in Complex III?


  It facilitates the transfer of electrons from CoQH₂ to cytochrome c.
• How does the Q cycle operate in Complex III?


  It involves two steps where one electron is transferred to cytochrome c at a time.
• What happens to protons during the Q cycle in Complex III?


  Two protons are released into the intermembrane space during the oxidation of CoQH₂.
• What are the key components of Complex III?


  • Two cytochrome b proteins
  • One cytochrome c protein
  • Rieske protein (FeS protein)
  • Two binding sites for CoQ (Q_p and Q_n)
• What is the significance of the intermembrane space in mitochondria?


  It is the space where protons accumulate to generate a proton gradient.
• What is the role of cytochrome c in the electron transport chain?

  Cytochrome c transfers electrons from Complex III to Complex IV.
• How does the electron transport chain contribute to ATP production?


  It generates a proton gradient that drives ATP synthesis via ATP synthase.
• How do the structures of the electron transport chain complexes relate to their functions?


  Complexes are large multi-subunit structures that facilitate electron transfer and proton pumping.
• What is the overall purpose of the electron transport chain and oxidative phosphorylation?


  To convert the reducing potential of NADH and FADH₂ into ATP.