Carbon monoxide, an odorless gas, combines with hemoglobin to form CO-hemoglobin
ID: 1069670 • Letter: C
Question
Carbon monoxide, an odorless gas, combines with hemoglobin to form CO-hemoglobin. Crystal of CO-hemoglobin are isomorphous with those of oxyhemoglobin. Each heme in hemoglobin can bind one carbon monoxide molecule, but O_2 and CO cannot simultaneously bind to the same heme. Exposure for one hour to a CO concentration of 0.1% in inspired air leads to the occupancy by CO of about half the heme sites in hemoglobin, a proportion that is frequency fatal. Problem: If the action CO were simply to diminish the oxygen-carrying power of the hemoglobin, without other modification of its properties, the symptoms of CO poisoning would be very difficult to understand in the light of other knowledge. Thus, a person whose blood is half-saturated with CO is practically helpless, but a person whose blood is half-saturated with CO is practically helpless, but a person whose hemoglobin percentage is simply diminished to half by anemia may be going about her work as usual. What is the answer to this Teeming paradox?Explanation / Answer
The binding of oxygen and CO2 to haemoglobin is a reversible process due to the shift is geometry of protein upon binding. On the other hand the binding of CO which is a smaller molecule fits inside the protein pocket and the bond formed with the complex is strong enough so as not to break at the later stage. This thus makes CO binding with haemoglobin an irreversible process and toxic to body. Person with anemia still has enough protein left for reversible O2/CO2 binding and release function and thus is able to live properly.