In eukaryotic cells, how does pyruvate produced by glycolysis enter the mitochondrial matrix for oxidation by the pyruvate dehydrogenase complex?

• A. It diffuses freely across the inner mitochondrial membrane because pyruvate is nonpolar at physiological pH.
• B. It is imported through the outer and inner mitochondrial membranes via the TOM and TIM protein translocases.
• C. It enters the matrix through the voltage-dependent anion channel (VDAC) in the outer membrane, which also spans the inner membrane.
• D. It is transported across the inner mitochondrial membrane by the mitochondrial pyruvate carrier (MPC), a specific pyruvate/H+ symporter.

Answer: (D)