Question

Read the assertion and reason carefully to mark the correct option in question.

Assertion: During ETS, four protons would be accumulated in the intermembrane space of mitochondria from one molecule of $FAD{H}_2$.

Reason: Ubiquinone receives reducing equivalents via $FAD{H}_2$.

• A. If assertion is true but the reason is false.
• B. If both assertion and reason are true but the reason is not the correct explanation of the assertion.
• C. If both assertion and reason are true and the reason is the correct explanation of the assertion.
• D. If both assertion and reason are false.

Answer 1

The correct option is B If both assertion and reason are true but the reason is not the correct explanation of the assertion.

Assertion-Reason relation

In TCA cycle, coupled reaction occurs where succinate converts into fumarate donating 2 electrons to complex II.

These 2 electrons and 2 hydrogen ions are picked up by FAD and become $FAD{H}_2$. These electron moves (one at a time) to an iron sulphur cluster, reduces $F{e}^{3+}$ to $F{e}^{2+}$. Once electrons are removed, $FAD{H}_2$ becomes FAD. $2H^{+}$ and 2 electrons are taken up by UQ.

Assertion-Reason relation

$UQ{H}_2$ gives up 2 electrons to complex III and 2 $H^{+}$. Protons are pumped out through complex III.

$2H^{+}$ from $UQ{H}_2$ move into Intermembrane space along with another $2H^{+}$ through the complex III. A total of $4H^{+}$ are transferred across the membrane.

Hence, both assertion and reason are true but the reason is not the correct explanation of the assertion.

Final answer

(B) If both assertion and reason are true but the reason is not the correct explanation of the assertion.