DAT Destroyer, Bio question #238

[j029337]

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DAT destroyer says that low pH increases hemoglobin affinity for O2.

I thought that the more basic the blood is, the higher the affinity because it shifts the curve to the left.
http://en.wikipedia.org/wiki/Oxygen-dissociation_curve

Their explanation/reasoning was that a low pH is due to increased CO2 levels. If CO2 levels increase, wouldn't that also be an increase in CO2 pressure? Is the explanation wrong or something because you can increase the acidity of blood via breakdown of fats/protein by your liver.

Is it correct that if you have more CO2 in your body, the CO2 pressure goes up and blood pH becomes more acidic? If your CO2 pressure goes up, then the hemoglobin affinity goes down, not up. Am I missing something here?

 

[yjdentist]

A decrease in pH means there is an increase in [H+].

High [H+] and higher CO2 levels decrease O2 affinity for Hb because when H+ binds to the Hb, there is a conformational change to the structure that favors the deoxy state of Hb, releasing O2 molecules.

The increase in CO2 level leading to decrease in pH is due to chemical equilibrium between protons and carbon dioxide in blood. Try dissolving CO2 in water, H2O+CO2--->H2CO3.

To make things simpler for myself, I try to think: if H and CO2 take the spot of O2 in Hb, then O2 has no where to go, and has to be released.

This effect is called Bohr effect. Read about that if you dont understand what I posted! 🙂

I am looking at my destroyer and the problem doesnt correspond. so i dont know what happened there, but yeah, low pH decreases the Hb affinity for O2.

 

[cm8a12321]

j029337:

Acidity in blood is based on the high concentration of CO2. However, hemoglobin does not attach to CO2 as easy as HCO3-. Thus, when there is high concentration of CO2, it really means that there is a high concentration of HCO3- in the blood.

Because of Bohr's effect, HCO3- is reduced back to CO2 in the capillaries of the lungs and expelled and loads up on O2 afterward.

This is why the hemoglobin curve is shifted to the right when blood is acidic.