Mechanism of cyanide poisoning is by inhibiting: NEET 13
**Core Concept**
Cyanide poisoning is a life-threatening condition caused by the ingestion or inhalation of cyanide compounds. It is a potent toxin that disrupts cellular respiration by inhibiting the electron transport chain in mitochondria.
**Why the Correct Answer is Right**
Cyanide binds to the iron atom in cytochrome c oxidase (Complex IV) of the electron transport chain, preventing the transfer of electrons and thereby halting oxidative phosphorylation. This leads to a rapid depletion of ATP, causing cellular dysfunction and ultimately cell death. The inhibition of Complex IV also shifts the electron transport chain to Complex I, leading to the production of reactive oxygen species (ROS) and further cell damage.
**Why Each Wrong Option is Incorrect**
**Option A:** This is incorrect because cyanide does not primarily inhibit Complex I of the electron transport chain. While Complex I is involved in the electron transport chain, cyanide's primary site of action is at Complex IV.
**Option B:** This is incorrect because cyanide does not primarily inhibit the sodium-potassium pump. Although the sodium-potassium pump is an essential ion pump, cyanide's mechanism of action is not through its inhibition.
**Option C:** This is incorrect because cyanide does not primarily inhibit the enzyme pyruvate dehydrogenase. While pyruvate dehydrogenase is an important enzyme in cellular respiration, cyanide's primary site of action is at Complex IV of the electron transport chain.
**Clinical Pearl / High-Yield Fact**
Cyanide poisoning is a classic example of a "high-iron" toxin, meaning that it binds to iron-containing enzymes such as cytochrome c oxidase. This makes it resistant to treatment with standard antidotes, and requires specific treatments such as hydroxocobalamin or sodium thiosulfate.
**Correct Answer:** C.