Question

In the process of ATP synthesis, oligomycin and DCCD act at which place in the figure:

A. A
B. B
C. C
D. D

Answer 1

Adenosine triphosphate (ATP) is the source of energy for cells driving them to perform their functions. The formation of ATP is mediated by ATP synthase.

Complete answer:
To arrive at a solution, the process of ATP synthesis is to be studied. ATP is formed in the mitochondria by the oxidative phosphorylation of adenosine diphosphate (ADP) with a release of protons as follows:
$ADP + Pi + 3{H^ + } \leftrightarrow ATP + H2O + 3{H^ + }$
However, this reaction is energetically unfavourable to produce ATP. To overcome this, the ATP synthase couples this process along with the electrochemical gradient formed across the inner membrane and mitochondrial matrix during cellular respiration. This is possible by ATP synthase because of the two units in it, namely: $F0$, an integral membrane protein complex which acts as a channel to protons and $F1$, a peripheral membrane protein complex which contains the binding site for the ATP synthesis. The passage of protons through $F0$ triggers the catalysis of ADP to ATP.
Oligomycin and N, $N'$-Dicyclohexylcarbodiimide (DCCD) are ATP synthase inhibitors. They act on the $F0$ subunit of ATP synthase, inhibiting ATP synthesis.

Hence, the correct answer is option (A).

Note: Oligomycin is a natural compound secreted by Streptomyces. They inhibit ATP synthesis by blocking the flow of protons. But they cannot completely block the flow due to the diffusion of protons through uncoupling protein. This phenomenon is known as proton leak.
DCCD is an inorganic compound. The ATP synthase has a rotatory mechanism for its production. DCCD causes steric hindrance to the rotating $F0$ subunit, which halts the synthesis.