Question

Given below are two statements, one is labelled as Assertion (A) and other one labelled as Reason (R).
Assertion (A) : Pericidine A, an antibiotic block the overall process of Electron transport chain (ETC).
Reason (R) : It inhibit electron flow from complex-I to Ubiquinone in electron transport chain.
In light of the above statements, choose the correct answer from the options given below.

• A. Both (A) and (R) are true and (R) is the correct explanation of (A).
• B. Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
• C. (A) is true but (R) is false.
• D. (A) is false but (R) is true.

Hint:

Remember the classic inhibitors of the ETC:
- Complex I: Rotenone, Amytal, and Piericidin A.
- Complex III: Antimycin A.
- Complex IV: Cyanide, Azide, Carbon Monoxide (CO).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The mitochondrial Electron Transport Chain (ETC) consists of a series of protein complexes (Complexes I-IV) that transfer electrons from donors to acceptors.
Specific inhibitors can bind to these complexes and block electron flow, halting ATP synthesis.

Step 2: Detailed Explanation:
- Assertion (A) is true:
Piericidin A (spelled "Pericidine A" in the question) is an antibiotic structurally similar to ubiquinone (coenzyme Q).
It acts as a potent inhibitor of the electron transport chain, blocking cellular respiration.
- Reason (R) is true:
Specifically, Piericidin A competes with ubiquinone for its binding site on Complex I (NADH:ubiquinone oxidoreductase).
By binding to Complex I, it prevents the transfer of electrons from the iron-sulfur (Fe-S) clusters of Complex I to ubiquinone.
Because Complex I is the entry point for electrons from NADH, blocking this initial step prevents the downstream flow of these electrons through the rest of the chain.
This halts the generation of the proton gradient across the inner mitochondrial membrane and blocks ATP synthesis.
Thus, the specific inhibition of electron flow from Complex I to Ubiquinone (R) is the direct explanation for why the overall ETC process is blocked (A).

Step 3: Final Answer:
Both (A) and (R) are true, and (R) is the correct explanation of (A).