Question

Thanks to cooperativity, hemoglobin subunits: (a) more readily bind O₂ when O₂ concentrations decrease in the blood, (b) more readily bind O₂ when O₂ concentrations increase in the blood, (c) dissociate (come apart) when O₂ concentrations decrease in the blood, (d) dissociate when O₂ concentrations increase in the blood, (e) all of the above.

Answer 1

We know that as pH decreases due to increase in pressure of CO2 (pCO2 ) it leads to decrease in the oxygen-binding capacity of hemoglobin, i.e. hemoglobin loses its oxygen molecules when concentration of O2 is less. Thus option (a) is incorrect. Option (b) is correct as O2 binds readily to hemoglobin as high O2 concentration. This can be explained by cooperativity, the binding affinity of hemoglobin towards oxygen increases when oxygen binds to one monomer of hemoglobin causing confirmational change in its structure resulting in increasing its affinity to bind to the next oxygen molecule. There is only confirmation change of hemoglobin occurs (R-T state change) when O2 binds or is released. Hence option (b) is the most appropriate answer.