Suppose that you are able to manipulate the potential of the...

Suppose that you are able to manipulate the potential of the inner membrane of an isolated mitochondrion. You measure the pH of the mitochondrial matrix and find it to be $8.0 .$ You measure the bathing solution and find its pH to be $7.0 .$ You clamp the inner membrane potential at $+59 \mathrm{mV}-$ that is, you force the matrix to be $59 \mathrm{mV}$ positive with respect to the bathing medium. Under these circumstances, can the mitochondrion use the proton gradient to drive the synthesis of ATP? Explain your answer in terms of the proton-motive force (see Section 5.6 to review)

Key Concepts

Proton-Motive Force

The proton-motive force is the energy generated by the combined effects of the membrane potential and the pH gradient across the inner mitochondrial membrane. It is the driving force that powers the ATP synthase enzyme, enabling the synthesis of ATP from ADP and inorganic phosphate. This force is quantitatively represented by contributions from the electrical gradient (voltage difference) and the chemical gradient (proton concentration difference).

Chemiosmotic Theory

The chemiosmotic theory explains how a proton gradient is used to synthesize ATP in mitochondria. According to this theory, the electron transport chain pumps protons across the inner mitochondrial membrane, thus creating an electrochemical gradient. ATP synthase harnesses the energy stored in this gradient (both pH difference and electrical potential) to drive the formation of ATP, highlighting the fundamental link between proton transit and energy production.

Membrane Potential

Membrane potential refers to the voltage across the mitochondrial inner membrane, created by the difference in charge distribution. This electrical potential is a critical component of the proton-motive force and contributes to the overall energy available to drive ATP synthesis. A higher internal potential relative to the exterior plays a key role in promoting the movement of protons back into the mitochondrial matrix.

pH Gradient

The pH gradient is the difference in proton concentration across the inner mitochondrial membrane. It represents a part of the proton-motive force by establishing a chemical gradient that facilitates the movement of protons. Since protons tend to move from areas of low pH (high concentration) to high pH (low concentration), this gradient is essential for driving the backflow of protons through ATP synthase, where their energy is transformed into ATP.

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