Why is NADH from the cytoplasm diffrent in term of energy yield than mitochondrial NADH?

Question

please help HW

Answer 1

Electrons from NADH in the cyoplasm require transport into the mitochondria. There are 2 general transporters, the malate aspartate shuttle, and the glycerol-3-phosphate shuttle. The malate aspartate shuttle takes the electrons from cytoplasmic NADH and puts them on mitochondrial NADH electron carriers, all fine and dandy, no energy yield lost. However, the glycerol-3-phosphate system, places the electrons from cytoplasmic NADH to mitochondrial FADH2, which is slight a loss in energy yield. I'm not exactly sure about which mechanism is selected and why, if it's 50-50, or random, or whatnot. But that is why there is decreased ATP yield (2 ATP/NADH vs 1.5 ATP/FADH2)