Question

Which one of the following binds with haemoglobin irreversibly?

• A. Carbon dioxide
• B. Carbon monoxide
• C. Ethane
• D. Nitrogen

Answer 1

The correct option is B Carbon monoxide

Hemoglobin contains four heme groups each capable of reversibly binding to one oxygen molecule. Oxygen binding to any of these sites causes a conformational change in the protein, facilitating binding to each of the other sites. Carbon monoxide binds to hemoglobin irreversibly at the same sites as oxygen, but approximately 200 times more tightly. Normally, oxygen would bind to hemoglobin in the lungs and be released in areas with low oxygen partial pressure (e.g., active muscles). When carbon monoxide binds to hemoglobin, it cannot be released as easily as oxygen. The slow release rate of carbon monoxide causes an accumulation of CO-bound hemoglobin molecules as exposure to carbon monoxide continues. Because of this, fewer hemoglobin particles are available to bind and deliver oxygen, thus causing the gradual suffocation associated with carbon monoxide poisoning. Thus, option B is correct.