Question

Four bacteria have been isolated from the soil, and each one uses a different final electron acceptor that is not oxygen. Which one will produce the most ATP per FADH2 molecule (E0 for FADH2 = -0.42V)

A. One that uses nitrite (E0 = +0.44V)

B. One that uses oxaloacetate (E0 = -0.166V)

C. One that uses H2 (E0 = -0.42V)

D. One that uses H2S (E0 = -0.3V)

Answer 1

In the question, we are provided with the reduction potentials of all the chemicals. We are taking it as standard for FADH2 which is given as -0.42V. Any substance that has a higher reduction potential than this will have a higher tendency to get reduced i.e. accepting more electrons.

In the given options, the most positive value as compared to that for FADH2 is of Nitrite (+0.44V), Thus it is the best electron acceptor among the four. The number of ATP molecules is directly proportional to the number of electrons transferred from FADH2 to the terminal electron acceptor.

Thus A. comes out to be the answer.