What is the effect of the following changes on the O ₂

Question

What is the effect of the following changes on the O ₂ affinity of hemoglobin?

A) A drop in the pH of blood plasma from 7.4 to 7.2.

a) Lower the O₂ Affinity. b) Increase the O₂ Affinity.

B) A decrease in the partial pressure of CO₂ in the lungs from 6 kPa (holding one's breath) to 2 kPa (normal).

a) Lower the O₂ Affinity. b) Increase the O₂ Affinity.

C) An increase in [BPG] from 5 mM (normal altitudes) to 8 mM (high altitudes).

a) Lower the O₂ Affinity. b) Increase the O₂ Affinity.

Accepted Answer

So here we have a 3 part practice problem broken up into part a, part b, and part c, and it's asking what is the effect of the following changes on the oxygen affinity of Hemoglobin? And so, Part A says, a drop in the pH of blood plasma from a value of 7 point 4 down to a value of 7.2. And of course, we know that a pH value of 7.2 is actually relatively acidic in comparison to a pH value of 7.4. And we also know from our previous lesson videos that a pH value of 7.2 actually corresponds with the pH of blood near the tissues. And so essentially, what we're saying here is that this scenario here in part a corresponds with hemoglobin's activity that we see in the tissues. And we know from our previous lesson videos that in the tissues, hemoglobin is going to release all of its oxygen so that all of these hard working muscle tissues can receive all of that released oxygen. And so what we're saying here is that this scenario corresponds with Hemoglobin releasing oxygen, and of course, released oxygen corresponds with a lowered affinity for oxygen. And so, because oxygen is being released in this scenario, we know that hemoglobin is gonna have a lower affinity for that oxygen. And so we can go ahead and cross off part b and indicate that the answer for part a is actually a. So now moving on to part b, it says, a decrease in the partial pressure of c o two in the lungs from 6 kilopascals, which would be holding one's breath, down to 2 kilopascals, which would be normal breathing. And so maybe part b threw you guys off because it gives us these very specific values of the partial pressure of c o 2. However, the exact values do not really matter so much for this part. Instead, what matters is that there's actually a decrease in the partial pressure of CO 2. So, 6 kilopascals is greater than 2 kilopascals, And so what this means is that the partial pressure is decreasing. And so if we have a decreased partial pressure of CO2, that means we're gonna have less c o two. And so what we need to recall from our previous lesson videos is that c o two acts as a heterotrophic allosteric inhibitor to hemoglobin's oxygen binding affinity. And so if c o two is acting as an inhibitor, and we have less of an inhibitor under these conditions, if we have less of an inhibitor, then we expect hemoglobin's activity to increase. And so that would correspond with increased oxygen affinity. And so, we can say that the answer for part b is actually going to be b. And so we can cross off option a. So now moving on to our last part of our question here, it says, an increase in the BPG concentration from 5 millimolar, at normal altitudes, up to a value of 8 millimolar at high altitudes. And so what we need to recall from our previous lesson videos is that BPG, similar to c o 2, is also a heterotrophic allosteric inhibitor. And so if we are increasing the amount of inhibitor going from 5 up to 8, that's increasing the amount of inhibitor. Of course, that means that, more of hemoglobin is going to be inhibited if we increase the amount of inhibitor. And that means that hemoglobin is gonna have a lower affinity for oxygen. And so we can go ahead and indicate that the answer for part c is a, and then we can cross off b. And so that concludes our 3 part practice problem and I'll see you guys in our next video.

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