Electron Transport Chain

Electron Transport Chain Overview

  • In aerobic metabolism, electrons are key for energy production.

  • The electron transport chain (ETC) is critical for ATP production, termed oxidative phosphorylation.

  • Oxygen is essential for this process, serving as a final electron acceptor.

Krebs Cycle Recap

  • Produces 1 ATP via substrate-level phosphorylation per cycle.

  • Generates high-energy carriers: NADH and FADH2.

  • NADH and FADH2 transport hydrogens and electrons to the ETC.

Structure of the Mitochondria

  • Mitochondrial structure: matrix, intermembrane space, and inner membrane.

  • The inner membrane is highly folded (cristae), increasing surface area for ETC proteins.

Key Proteins in the Electron Transport Chain

  • Complex I (NADH Dehydrogenase)

    • Accepts electrons from NADH, recycling NAD+.

    • Pumps protons (H+) from the matrix to the intermembrane space.

  • Complex II

    • Transfers electrons from FADH2 to the chain (not a proton pump).

  • Complex III

    • Accepts electrons from Complex I and II, and pumps protons into the intermembrane space.

  • Complex IV

    • Transfers electrons to oxygen, producing water and facilitating proton pumping.

Proton Gradient Formation

  • Electrons moving through the ETC drive proton pumps, creating a proton gradient across the inner membrane.

  • The gradient creates potential energy, which is utilized for ATP synthesis.

ATP Synthesis via Chemiosmosis

  • ATP Synthase

    • Utilizes the proton gradient to convert ADP and inorganic phosphate into ATP.

    • H+ ions flow back into the matrix, releasing energy converted to kinetic energy to synthesize ATP.

  • Chemiosmotic Hypothesis

    • Explains how the proton gradient leads to ATP production.

Energy Yield from NADH and FADH2

  • Electrons from NADH: pump 3 protons; yield approximately 2.5 ATP.

  • Electrons from FADH2: pump 2 protons; yield approximately 1.5 ATP.

Role of Oxygen

  • Oxygen is the final electron acceptor in the ETC.

  • Combines with electrons and protons to form water.

  • Absence of oxygen leads to the cessation of ATP production via oxidative phosphorylation due to buildup in the ETC.

Overall Reaction of Glucose Oxidation

  • Glucose (C6H12O6) + Oxygen (O2) -> Carbon Dioxide (CO2) + Water (H2O) + ATP + Heat

  • Balanced reaction results in: 6 CO2, 6 H2O, and requires 6 O2.

  • Approximately 34 ATP can be produced through oxidative metabolism of one glucose molecule.