Cyanide and electron transfer

Question

When people ingest cyanide ion, the cyanide binds strongly to the enzyme that transfers electrons from cytochrome c to oxygen.  

This blocks the enzyme from functioning.

Why does this cause death so quickly? 

Cyanide poisoning victims often feel like they are suffocating and breathe deeply and rapidly before death. Why do you think they respond 

this way?

The victims are often diagnosed by having very high blood lactate levels. Why does this occur?

People suffering from nonfatal cyanide poisoning are often treated by being administered 100% oxygen. Why does this help them recover?

Answer 1

Important background information: In the electron transport chain, electrons are donated by NADH or FADH2 to complexes I and II respectively. After this, those electrons flow to coenyzyme Q, complex III, cytochrome C, complex IV, and finally onto O2 which can then become H2O. During this electron transfer, complexes I, III, and IV can pump protons out of the matrix, setting up a concentration gradient that provides the energy for ATP synthesis.

Where the problem comes in: When you prevent electrons from reaching O2, the system backs up. Think of the electrons as flowing down a river from complex to complex, and now you've placed a barrier right in between cytochrome c and complex IV. When this happens, electrons can no longer flow, and now protons can no longer be pumped out of the matrix. This means that we no longer have energy to produce ATP, causing a rapid loss of energy within the body.

Since the ETC uses oxygen it is a form of aerobic respiration, but since no oxygen is being used, the body tries to compensate by breathing deeper. This is also why providing 100% oxygen can alleviate some minor cyanide poisoning. Similarly, since aerobic respiration is not working, glycolysis (an anaerobic process) will ramp up to try and compensate. It will then finish at it's anaerobic end point, lactate fermentation, which produces a lot of lactate, instead of ending aerobically at pyruvate.