Cyanide is toxic because it –
**Core Concept**
Cyanide is a highly toxic substance that exerts its lethal effects through a mechanism that disrupts cellular respiration. This occurs at the mitochondrial level, where cyanide binds to the cytochrome c oxidase enzyme, thereby preventing the transfer of electrons and halting the production of ATP.
**Why the Correct Answer is Right**
Cyanide binds to the iron atom within cytochrome c oxidase, a key enzyme in the electron transport chain. This binding event blocks the transfer of electrons from cytochrome c to oxygen, effectively halting oxidative phosphorylation and ATP production. As a result, cells become unable to generate energy, leading to cellular dysfunction and ultimately, cell death.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because cyanide's mechanism of toxicity is not related to its ability to interfere with protein synthesis or DNA replication.
**Option B:** This option is incorrect because cyanide does not act as a competitive inhibitor of acetylcholinesterase, which is the target of organophosphate poisoning.
**Option C:** This option is incorrect because cyanide's mechanism of toxicity is not related to its ability to induce oxidative stress through the generation of reactive oxygen species.
**Clinical Pearl / High-Yield Fact**
Cyanide poisoning is a medical emergency that requires prompt treatment with antidotes such as hydroxocobalamin or sodium thiosulfate. These agents work by binding to cyanide and facilitating its excretion from the body.
**Correct Answer: D.**