Chemiosmosis Simulation (ATP Production in Mitochondria)

Chemiosmotic Hypothesis Mitchell 1961

Electrochemical Proton-Motive Force ($\Delta p$) & Rotary ATP Synthesis in Mitochondria

● STATE 3: COUPLED PHOSPHORYLATION

PMF: 218 mV

Protons (H⁺)

Electrons (2e⁻)

ATP Generated

Inhibited Complex

Click canvas to inject test protons • Tap complexes for biochemical inspection

Chemiosmotic Metrics

0 ATP synthesized

Total PMF ($\Delta p$)

218 mV

Electrical ($\Delta\Psi$):

+165 mV

Chemical ($-59\Delta\text{pH}$):

+53 mV

IMS pH (Acidic)

7.02 [P-side]

Matrix pH (Alkaline)

7.92 [N-side]

ATP Synthase Rotation

124 rev/sec

Synthesis Rate

372 ATP/sec

Substrate Supply

NADH Influx Rate 80%

Provides high-energy 2e⁻ to Complex I (NADH Dehydrogenase).

Terminal Acceptor [O₂] 100%

Essential terminal electron sink at Complex IV ($O_2 + 4H^+ \rightarrow 2H_2O$).

Chemical Inhibitors & Uncouplers

The Chemiosmotic Hypothesis

Peter D. Mitchell (Nobel Prize in Chemistry, 1978)

The Core Principle

Prior to Mitchell’s 1961 paper, biochemists sought a mysterious "high-energy chemical intermediate" (similar to substrate-level phosphorylation). Mitchell revolutionized bioenergetics by proving that energy coupling is vectorial and spatial.

Proton-Motive Force ($\Delta p$):
$\Delta p = \Delta\Psi - \left(\frac{2.303 \cdot R \cdot T}{F}\right) \Delta\text{pH} \approx \Delta\Psi - 59\,\Delta\text{pH} \text{ (mV)}$

Step-by-Step Mechanism

1. Oxidation of Substrates: High-energy electrons from NADH/FADH₂ enter Complex I/II.
2. Directional Proton Pumping: As electrons fall through thermodynamic redox cascades across Complex I, III, and IV to molecular Oxygen ($O_2$), protons are pumped from the matrix to the intermembrane space (IMS).
3. Electrochemical Gradient: The inner mitochondrial membrane is impermeable to free ions, building a steep charge ($\Delta\Psi \approx 160-180\text{ mV}$) and chemical gradient ($\Delta\text{pH} \approx 0.8-1.0$).
4. Rotary Chemiosmosis: Protons re-enter the matrix exclusively down their electrochemical gradient via the $F_o$ subcomplex of ATP Synthase, rotating the rotor shaft and catalyzing $ADP + P_i \rightarrow ATP$ at the $F_1$ catalytic head.

Pharmacological Perturbations in this Simulation

• Cyanide (CN⁻): Binds cytochrome $a_3$ in Complex IV, freezing electron transport. Pumping ceases; PMF rapidly decays.
• Oligomycin: Plugs the proton pore of the $F_o$ subunit. ATP synthesis stops immediately, and the membrane hyperpolarizes as back-pressure halts the ETC.
• 2,4-Dinitrophenol (DNP): A lipophilic protonophore (uncoupler). It ferries protons across the bilayer directly, bypassing ATP Synthase. PMF collapses, synthesizing 0 ATP, while ETC operates at maximal futile speed, dissipating energy as heat.