Correct option is D
The correct answer is transport of NADH from the cytosol into the mitochondrial matrix, as this process does not directly involve the proton motive force (PMF). Instead, NADH generated in the cytosol during glycolysis cannot cross the inner mitochondrial membrane directly. To overcome this, cells use shuttle systems such as the malate-aspartate shuttle or the glycerol-3-phosphate shuttle, which transfer reducing equivalents (electrons), not the NADH molecule itself.
These shuttles work independently of the proton motive force generated by the electron transport chain. In contrast, the movement of ATP, ADP, and phosphate across the mitochondrial membrane is facilitated by specific transporters like ATP/ADP translocase and phosphate translocase, both of which utilize the electrochemical gradient (PMF) across the inner mitochondrial membrane.
Additional Information:
- (a) Transport of ATP into the cytosol from mitochondrial matrix: This process is carried out by the ATP/ADP translocase, which relies on the electrical component of the proton motive force for driving the exchange of negatively charged ATP⁴⁻ with ADP³⁻.
- (b) Transport of ADP from the cytosol into the mitochondrial matrix: This occurs via the same translocase system and is coupled with ATP export, driven by the membrane potential component of PMF.
- (c) Transport of phosphate ions from the cytosol into the mitochondrial matrix: This is facilitated by the phosphate-H⁺ symporter, which uses the proton gradient (part of PMF) to drive the uptake of phosphate into the matrix for ATP synthesis.
