Cyanide (CN-) closely resembles molecular oxygen, and binds tightly to cytochrome C oxidase, the electron carrier that reduces O2 during aerobic respiration. Brain cells cannot ferment glucose, and therefore have to respire to utilize glucose. Cyanide is deadly to brain cells because in its presence:

Cyanide is deadly to brain cells because in its presence, the mitochondria of brain cells are unable to produce ATP from glucose metabolism due to inability to transfer electrons to oxygen and NAD⁺ cannot be generated from NADH as shown in the reactions below:

ADP + Pi ---> ATP

NADH + H⁺ + 1/2O₂  > NAD⁺ + H₂O

This results in symptoms such as dizziness, fainting, coma and ultimately death.

Explanation:

Cyanides are compounds containing a carbon-nitrogen (CN⁻) bond. Although many substances contain cyanide, but not all of them are toxic. Sodium cyanide (NaCN), potassium cyanide (KCN), hydrogen cyanide (HCN), and cyanogen chloride (CNCl) are lethal poisons which when ingested above a certain dose, result in rapid death.

Cyanide inhibits the mitochondrial electron transport chain  within cells and renders the body unable to produce ATP from oxygen. It  specifically binds to the a3 portion (complex IV) of cytochrome C oxidase , the electron carrier that reduces O₂ during aerobic respiration thereby preventing cells from using oxygen, causing rapid death.

Cyanide is deadly to brain cells because in its presence, the mitochondria of brain cells are unable to produce ATP from glucose metabolism due to inability to transfer electrons to oxygen and NAD⁺ cannot be generated from NADH as shown in the reactions below:

ADP + Pi ---> ATP

NADH + H⁺ + 1/2O₂  > NAD⁺ + H₂O

This results in symptoms such as dizziness, fainting, coma and ultimately death.

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