Question

Assuming the electron transport chain received electrons from NADH and FADH₂ in a 3:1 ratio as the wild type for a particular organism, what would the consequences be of a change to a 1:1 ratio? Select all that apply.

Answer 1

If the ratio of electrons received from NADH and FADH2 in the electron transport chain reduced from 3:1 to 1:1 ,

the net synthesis of ATP molecules would decrease.

Each NADH molecule pumps 4 protons, and each FADH2 molecule pumps 2 protons. A total of 8 protons are required for the synthesis of one ATP molecule.

Let us say a total of 30 electrons are transported , of which 20 are from NADH and 10 are from FADH2 (3:1).

For each two electrons transported by NADH, 4 protons are pumped. Thus for 20 electrons, 40 protons will be pumped. For each two electrons transported by FADH2, 2 protons will be pumped. Thus, for 10 electrons, 10 electrons will be pumped. Thus a total of 50 protons will be pumped, thus producing 6.25 ATP molecules.

If the ratio of electrons transported is 1:1, then number of electrons transported by NADH and FADH2 are 15 each.

Thus number of protons pumped are 14 and 7 respectively,i.e., a total of 21. As the synthesis of one ATP molecule requires 8 protons , the number of ATP molecules produced in this case is less than 3.

Thus, a change in the ratio of electrons received from NADH and FADH2 in the electron transport chain from 3:1 to 1:1 would reduce the net synthesis of ATP molecules .