Electron transport chain and ATP synthase template

Complexes I–IV in the inner mitochondrial membrane with coenzyme Q and cytochrome c, protons pumped 4/4/2 per NADH, O₂ reduced to water and ATP synthase (F₀F₁) driven by the returning protons; ubiquinone/ubiquinol structures.

What the template shows

• Electrons from NADH and FADH₂ flow to O₂; the proton gradient they build drives ATP synthesis (chemiosmosis)
• Inner mitochondrial membrane
• Protons pumped per NADH (2 e⁻): 4 by complex I, 4 by complex III, 2 by complex IV
• Intermembrane space · high [H⁺], + side
• inner mitochondrial membrane
• NADH–Q oxidoreductase
• succinate dehydrogenase
• Q–cyt c oxidoreductase
• cytochrome c oxidase
• ATP synthase
• ADP + Pᵢ → ATP
• NADH → NAD⁺ + H⁺
• succinate → fumarate
• FAD → FADH₂ in II
• ≈ 3 H⁺ per ATP
• Matrix · low [H⁺], − side
• Coenzyme Q carries two electrons and two protons
• R = isoprenoid tail (10 isoprene units in humans, CoQ₁₀): it keeps Q in the membrane
• Per NADH 10 H⁺ are pumped (≈ 2.5 ATP); per FADH₂ from succinate, entering at complex II (no pumping), 6 H⁺ (≈ 1.5 ATP).
• Q (in the membrane) and cytochrome c (on the outer face of the inner membrane) are the mobile carriers.
• Complex IV: O₂ + 4 e⁻ + 4 H⁺ (matrix) → 2 H₂O; cyanide, CO and azide block it, and rotenone blocks complex I.
• Mitchell’s chemiosmosis: H⁺ flowing back through F₀ turns the c ring and F₁ makes ATP (binding change); ≈ 3 H⁺ per ATP plus 1 H⁺ to import Pᵢ.

Drawn with 28 atoms, 1 arrow, 53 shapes – every one editable in MolDraw.

Sources

• Nelson & Cox, Lehninger Principles of Biochemistry, 8th ed., 2021 Textbook
• Berg, Tymoczko, Gatto & Stryer, Biochemistry, 9th ed., 2019 Textbook
• Voet & Voet, Biochemistry, 4th ed., Wiley 2011 Textbook
• Mitchell, Nature 1961, 191, 144 Original paper