11. Proton motive force during oxidative phosphorylation is generated in mitochondria by
(1) exchanging protons for sodium ions
(2) pumping protons out into intermembrane space
(3) pumping hydroxyl ions into the mitochondria
(4) hydrolysis Of ATP

 

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The proton motive force (PMF) is a vital component of cellular energy production in eukaryotic cells. It is the electrochemical gradient of protons (H⁺ ions) across the mitochondrial inner membrane that powers ATP synthesis during oxidative phosphorylation. Understanding how this force is generated is key to grasping the bioenergetics of cellular respiration.

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What Is Proton Motive Force?

Proton motive force is the combined effect of two gradients across the mitochondrial inner membrane:

• An electrical gradient (membrane potential, Δψ), due to charge separation.

• A chemical gradient (proton concentration difference, ΔpH), due to differing proton concentrations on either side of the membrane.

Together, these gradients store potential energy used by ATP synthase to convert ADP and inorganic phosphate into ATP.

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How Is Proton Motive Force Generated?

During oxidative phosphorylation, electrons from NADH and FADH2 pass through the electron transport chain (ETC) complexes embedded in the mitochondrial inner membrane. The energy released from these electron transfers is harnessed to actively pump protons from the mitochondrial matrix into the intermembrane space.

This proton pumping creates:

• A high concentration of protons in the intermembrane space.

• A lower proton concentration in the matrix.

• An electrical potential difference due to the positive charge of protons.

This electrochemical gradient constitutes the proton motive force.

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Why Proton Pumping Into the Intermembrane Space?

• The mitochondrial inner membrane is impermeable to protons, allowing the gradient to be maintained.

• Pumping protons out of the matrix into the intermembrane space stores energy that can be used to drive protons back through ATP synthase.

• The flow of protons back into the matrix through ATP synthase provides the energy needed for ATP production.

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Evaluating the Options

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Summary

• The proton motive force in mitochondria is generated by pumping protons from the matrix into the intermembrane space during electron transport.

• This creates an electrochemical gradient used by ATP synthase to produce ATP.

• The process is central to cellular energy metabolism and is described by the chemiosmotic theory.

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Final Answer:

(2) Pumping protons out into intermembrane space