A: Potassium cyanide when consumed causes death by gradually arresting the supply of oxygen to our body’s cells by forming complexes with haemoglobin and cytochrome (a protein which helps in the respiration of cells), depriving them of their capacity to transport or exchange oxygen.
Normally, oxygen is carried to different parts of the body from the lungs by the blood using haemoglobin — the iron-containing, oxygen-carrying molecule of the red blood cells.
Haemoglobin is made up of a globular protein and four heme groups. The iron (in ferrous state) present in these heme complexes can bond to either an oxygen molecule or a water molecule or exchange one for the other without much difficulty. It is because of this ability that haemoglobin is able to pick up oxygen from the lungs, carry it to the cells, and bring water in return.
Cells respire oxygen with the help of myoglobin (haemoglobin-like proteins present in the cells) and cytochrome, which carries electrons. Specific forms of cytochrome and haemoglobin also cause sudden death when poisoned by cyanide.
When potassium cyanide is consumed, it splits into a potassium ion and a cyanide ion. The cyanide ion has a greater affinity for the ferrous ion than. As a result it occupies the site meant for oxygen in haemoglobin. This process is irreversible and prevents the transfer of oxygen.
One form of cytochrome, designated cytochrome-a, also binds with the cyanide ion and stabilises the iron to such an extent that it does not take part in the electron transfer to the cell. This prevents oxygen intake by the cell.
The symptoms of cyanide poisoning are giddiness, headache, and bluish tinge of the skin. If not treated immediately, unconsciousness and death will follow.
A. Karthikeyani, Udumalpet; C. Ravi Chandra, Secunderabad; and R. Ramaa, Chennai
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