Which shuttle more efficiently transfers reducing equivalents into mitochondria?

Which shuttle more efficiently transfers reducing equivalents into mitochondria?

• A. Glycerol-3-phosphate shuttle
• B. Malate-aspartate shuttle
• C. Both equally efficient
• D. Neither transfers NADH equivalents

Answer: (B)

The main idea is how each shuttle delivers reducing equivalents into the mitochondrial matrix where they can be used to generate ATP. NADH itself cannot cross the inner mitochondrial membrane, so cells use shuttles to move those reducing equivalents as other metabolites. The malate-aspartate shuttle is more efficient because it moves the reducing equivalents into the matrix in the form of NADH. Malate carries the electrons into the matrix, where malate dehydrogenase converts NAD+ to NADH inside the mitochondrion, preserving the higher-energy carrier. The cycle continues with transamination steps to return to cytosolic forms. Since the matrix NADH can feed into Complex I, this pathway yields more ATP per cytosolic NADH (roughly equivalent to the NADH energy yield). The glycerol-3-phosphate shuttle, on the other hand, transfers electrons to FAD to form FADH2 within the inner membrane, and FADH2 donates electrons at a lower energy level, bypassing Complex I. This results in a smaller ATP yield per cytosolic NADH. So, the malate-aspartate shuttle is the more efficient route for transferring reducing equivalents into mitochondria.

The main idea is how each shuttle delivers reducing equivalents into the mitochondrial matrix where they can be used to generate ATP. NADH itself cannot cross the inner mitochondrial membrane, so cells use shuttles to move those reducing equivalents as other metabolites.

The malate-aspartate shuttle is more efficient because it moves the reducing equivalents into the matrix in the form of NADH. Malate carries the electrons into the matrix, where malate dehydrogenase converts NAD+ to NADH inside the mitochondrion, preserving the higher-energy carrier. The cycle continues with transamination steps to return to cytosolic forms. Since the matrix NADH can feed into Complex I, this pathway yields more ATP per cytosolic NADH (roughly equivalent to the NADH energy yield).

The glycerol-3-phosphate shuttle, on the other hand, transfers electrons to FAD to form FADH2 within the inner membrane, and FADH2 donates electrons at a lower energy level, bypassing Complex I. This results in a smaller ATP yield per cytosolic NADH.

So, the malate-aspartate shuttle is the more efficient route for transferring reducing equivalents into mitochondria.