Question

In electron transport, which respiratory complex is not involved in the flow of electrons from NADH?

A) complex I
B) complex II
C) complex III
D) complex IV
E) all of the above

Answer 1

In electron transport, complex II is not involved in the flow of electrons from NADH, as it directly receives electrons from FADH2 and does not pump protons across the membrane.

Step-by-step explanation:

In the electron transport chain, complex II is the respiratory complex not involved in the flow of electrons from NADH. Instead of receiving electrons from NADH, complex II directly receives electrons from FADH2 through a small complex that delivers the electrons directly to the electron transport chain, bypassing complex I.

Unlike complexes I, III, and IV, complex II does not pump protons across the mitochondrial inner membrane, although it does contribute to the electron transport chain by transferring electrons to ubiquinone (Q), which then moves the electrons to complex III.

The critical role of ubiquinone is to connect the first and second complexes to the third, transferring electrons from both NADH (via complex I) and FADH2 (via complex II) to complex III.