In the body, hemoglobin (Hb) is the substance responsible for transporting oxyge

Question

In the body, hemoglobin (Hb) is the substance responsible for transporting oxygen (O_2) to tissues. Hemoglobin binds oxygen to produce oxyhemoglobin (HbO_2): Hb + O_2 lrharHbO_2 Carbon monoxide (CO) can also bind to hemoglobin to produce carboxyhemoglobin (HbCO): Hb + CO lrhar HbCO The equilibrium constant for Reaction (2), Koo, is about 210 times larger than the equilibrium constant for Reaction (1), KO_2. Thus, carbon monoxide binds to hemoglobin much more efficiently than oxygen. KCO/KO_2 = 210 Write a balanced equation for the displacement of oxygen from HbO_2 by CO to produce HbCO. Write the equilibrium constant expression for your overall reaction. Write an equation that relates the equilibrium constant for the overall reaction described in part (a) to the equilibrium constants KCO and KO_2 Use your balanced equation from part (a) and your knowledge of equilibrium constants to explain why patients who are experiencing CO poisoning are generally given pure oxygen as a remedy.

Explanation / Answer

a)

The reaction has a ratio 1:1 so:

HbO2 + CO <--> O2 + HbCO

K = [O2][HbCO]/([CO][HbO2]

b

relate

constants:

K1

Hb + CO <--> HbCO K1

Hb + O2 <--> HbO2 K2

invert

HbO2 <--> Hb + O2 1/K2

so

Hb + CO <--> HbCO K1

HbO2 <--> Hb + O2 1/K2 is true

add both

HbO2 + CO <--> HbCO + O2 K = (K1/K2)

then

K = 210

c)

if we add O2, then we will favour the reverse shift, that is, addition of O2 is competing for Hb as well

so

HbCO + O2 excess ---> HbO2 + CO

so this will "free" HB hemoglobin of CO and get O2 which is required for human respiration

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