Question

In electron transport chain, when $FAD{H}_2$ is oxidized to $FAD$, the electrons are passed to cytochrome proteins where as hydrogen ions are released into:

• A. Matrix
• B. Cytosol
• C. Outer membrane
• D. Perimitochondrial space

Answer 1

The correct option is D Perimitochondrial space

The electron transport system occurs in the inner membrane of the mitochondria.

When electrons pass from one carrier to another via complex I to IV, in the electron transport chain, they are coupled to ATP synthase (complex V) for the production of ATP.

Energy released during the passage of electrons from one carrier to the next is made available to specific transmembrane complexes, which pump protons $\left(H^{+}\right)$ from the matrix side of the inner mitochondrial space (perimitochondrial space) to the outer chamber or cytosol.

Transport of the electrons from $NADH$ over $ETC$ helps in pushing three pairs of hydrogen ions (protons) to the perimitochondrial space, while two pairs of protons (hydrogen ions) are sent outwardly towards perimitochondrial space, during electron flow from $FAD{H}_2$ (as the latter donates its electrons further down to the ETC).

Thus, option d is the correct answer.