23. Cyanide, a chemical warfare agent, is toxic because it:
A. binds to the heme a3 in mitochondrial cytochrome C oxidase (in complex IV)
B. inhibits electron transport and thus oxidative phosphorylation
C. directly blocks mitochondrial DNA replication
D. blocks the protein trafficking inside the
mitochondria by affecting TIM and TOM channels
Choose the combination with all correct statements.
(1) A and C         (2) A and B
(3) B and C         (4) A, B and D

 

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Cyanide is a potent chemical toxin and warfare agent primarily because of its effect on cellular respiration. Its toxicity arises from interference with mitochondrial function, specifically targeting the electron transport chain.

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Correct Statements About Cyanide Toxicity

• (A) Cyanide binds to the heme a3 in mitochondrial cytochrome c oxidase (Complex IV):
  Cyanide binds strongly to the heme a3 iron center in Complex IV (cytochrome c oxidase), blocking the transfer of electrons to oxygen, the final electron acceptor. This prevents cellular respiration from proceeding.

• (B) Cyanide inhibits electron transport and thus oxidative phosphorylation:
  By blocking Complex IV, cyanide halts electron flow through the electron transport chain, stopping proton pumping and ATP synthesis. This causes rapid depletion of cellular ATP and energy failure.

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Incorrect Statements

• (C) Cyanide directly blocks mitochondrial DNA replication:
  There is no evidence that cyanide directly interferes with mitochondrial DNA replication. Its primary toxicity is at the level of electron transport inhibition.

• (D) Cyanide blocks protein trafficking inside mitochondria by affecting TIM and TOM channels:
  Cyanide does not affect mitochondrial protein import machinery (TIM and TOM complexes). Its toxicity is related to respiratory inhibition.

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Summary Table

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Final Answer:

(2) A and B