Question

Which statement best explains why NADH produces more ATP per molecule than a molecule of FADH${}_2$?

• A. There is more NADH than FADH${}_2$made for every glucose that enters cellular respiration.
• B. The H+ gradient made from electron transport using NADH is located in a different part of the mitochondrion than the H+ gradient made using FADH${}_2$.
• C. Fewer protons are pumped across the inner mitochondrial membrane when FADH${}_2$ is the electron donor than when NADH is the electron donor.
• D. It takes more energy to make ATP from ADP and P${}_i$ using FADH${}_2$ than using NADH.

Answer 1

Answer: (C)

Fewer protons are pumped across the inner mitochondrial membrane when FADH${}_2$ is the electron donor than when NADH is the electron donor.

In the electron transport system the last step of respiration occurs in mitochondria of a cell and includes various electron carrying complexes and NADH produces more electron as it gives its electron to complex I which further passes to complex III and energy is given out to pump the electrons which create a gradient and then the electron passes to complex IV while FADH starts this process with complex II. As NADH starts it with complex I it has more chance to pump proton across the gradients which increase the ATP synthase and hence produce more ATP than FADH which collects two protons by reducing its path to complex II.

So, the correct answer is 'Fewer protons are pumped across the inner mitochondrial membrane when FADH2 is the electron donor than when NADH is the electron donor'.