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.

Correct option is B

Explanation-

Statement A  -  Binds to the heme a3 in mitochondrial cytochrome c oxidase (in complex IV)  - CORRECT
​Cyanide binds with high affinity to the heme a3 center of cytochrome c oxidase (Complex IV) in the mitochondrial electron transport chain. This binding prevents the reduction of oxygen, halting cellular respiration.
Statement B - Inhibits electron transport and thus oxidative phosphorylation  - CORRECT
Because cyanide blocks Complex IV, electron flow is stopped. This leads to failure of proton pumping, halting ATP synthesis through oxidative phosphorylation. This is the main mechanism of cyanide toxicity.
Statement C - Directly blocks mitochondrial DNA replication - INCORRECT
Cyanide does not directly affect mtDNA replication. Its primary action is on the electron transport chain, not DNA processes.
Statement D - Blocks the protein trafficking inside the mitochondria by affecting TIM and TOM channels  - INCORRECT
Cyanide does not interfere with TIM (Translocase of Inner Membrane) or TOM (Translocase of Outer Membrane). These channels are for protein import; cyanide does not target them.

Correct Combination: A and B → Option b 
Final Answer: Option b: A and B is correct.