Question

Cytoplasmic NADH is oxidatively phosphorylated inside mitochondrion. Mitochondrion is impermeable to NADH. Entry into mitochondrion is effected through

• A. Shuttle system
• B. Facilitated diffusion
• C. Active absorption
• D. $F_0$ tunnel of elementary particles

Answer 1

Answer: (A)

Shuttle system

NADH molecules are synthesized in the cytoplasm by the process of glycolysis. However, the NADH molecules cannot cross the mitochondrial membrane to translocate its electrons to the electron transport chain in the mitochondrial matrix. This has been made possible by means of a shuttle system because the mitochondrial inner membrane is impermeable to NADH. In this system, malate carries the reduction equivalents across the membrane and is known as malate-aspartate shuttle system.

Thus, the correct answer is option A.