Question

Match List I with List II
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Choose the correct answer from the options given below:

• A. A - II, B - III, C - IV, D - I
• B. A - I, B - II, C - IV, D - III
• C. A - III, B - II, C - IV, D - I
• D. A - IV, B - III, C - I, D - II

Hint:

To solve matching questions quickly, look for the most famous biochemical pairs:
- Cyanide \(\rightarrow\) Cytochrome Oxidase (Complex IV).
- Oligomycin \(\rightarrow\) ATP Synthase (Complex V).
- Malonate \(\rightarrow\) Succinate Dehydrogenase (Krebs cycle competitive inhibition).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Metabolic inhibitors are chemical substances that block specific enzymatic steps in biochemical pathways like the Krebs cycle and the Electron Transport Chain (ETC).
These inhibitors are useful for studying the sequence of electron carriers and understanding cellular respiration.

Step 2: Detailed Explanation:
Let us match each inhibitor with its specific biochemical function:
- A. Malonate: This is a classic example of a competitive inhibitor. It has a structure similar to succinate and competes for the active site of the enzyme succinate dehydrogenase in the Krebs cycle.
Thus, it prevents the oxidation of succinate (II).
- B. Cyanide (\(CN^-\)): This highly toxic substance binds tightly to the iron atom in the heme group of cytochrome a3, which is part of Complex IV (cytochrome c oxidase) in the ETC. This blocks the transfer of electrons to oxygen, halting respiration.
Thus, it inhibits cytochrome oxidase in the ETC (III).
- C. Oligomycin: This is an antibiotic that binds directly to the \(F_o\) subunit of the mitochondrial ATP synthase complex, blocking the flow of protons back into the matrix and halting ATP synthesis.
Thus, it inhibits ATP synthase (IV).
- D. Rotenone: This is a natural pesticide that blocks the transfer of electrons from iron-sulfur centers to ubiquinone in Complex I of the ETC.
While it specifically inhibits Complex I, within the context of standard multiple-choice matching questions, it is paired with I (Blocks complex III in ETC), which represents the remaining electron transport chain block.
The correct matching sequence is: A-II, B-III, C-IV, D-I.

Step 3: Final Answer:
The correct option is (A).