Mitochondrial Function and Electron Transport Chain

Overview of Eukaryotic Cells

• Eukaryotic cells contain membrane-bound organelles.
• Mitochondria are key organelles with double membranes.
• Primary function: Harness energy for cell growth and reproduction.

Mitochondrial Structure

• Inner Mitochondrial Membrane
  • Acts as a barrier to protons, maintaining a concentration gradient.
  • Contains F1F0 ATP synthase protein complex.
  • Proton gradient drives ATP synthesis, essential for cell reactions.

ATP Synthase Function

• Similar to power plants using flow to rotate turbines.
• Proton flow across the membrane rotates protein subunits to synthesize ATP.
• Without a proton gradient, ATP synthesis halts, leading to energy starvation.

Electron Transport Chain (ETC)

• Composed of four protein complexes (1 to 4).
• Complexes 1, 3, and 4 pump protons from matrix to intermembrane space.
• Complex 2 does not pump directly but aids complexes 3 and 4.
• Energy for proton pumping comes from electron transfer through coupled reactions.

Complex I

• NADH deposits two high-energy electrons.
• Electrons pass through redox centers.
• Redox centers have varying electron affinities, facilitating electron flow.
• Energy from electron transfer is used to pump protons.
• Last redox center donates electrons to Coenzyme Q.

Complex II

• Electrons enter via FADH2.
• Similar redox center transfer process.
• Does not pump protons.
• Donates electrons to Coenzyme Q.

Coenzyme Q and Complex III

• Receives electrons from Complexes I and II.
• One electron is recyclable.
• Transfers electrons to cytochrome C.

Complex IV

• Cytochrome C carries electrons here.
• Converts oxygen to water, incorporating protons into water molecules.
• Pumps additional protons to intermembrane space.
• Oxygen serves as final electron acceptor.

Importance of Oxygen

• Essential for electron transfer continuation.
• Absence of oxygen halts electron transfer and ATP synthesis.
• Cellular respiration relies on oxygen as the final electron acceptor.

Mitochondrial Efficiency

• Protein complexes are densely packed in the inner membrane.
• Entire membrane acts as a cellular power plant.