What happens when the pH decreases during cellular respiration? What effect does this have on the hemoglobin’s affinity? What is the Bohr effect?
You can find the answers on this video as Leslie explains more about what happens during cellular respiration.
Transcript of Today’s Episode
Hello and welcome to another episode of Interactive-Biology T.V. where we’re making Biology fun! My name is Leslie Samuel and in this episode, Episode 61, I’m going to be explaining the Bohr Effect. So, let’s get right into it.
Now, we’ve looked at this oxygen dissociation curve of hemoglobin in Episode 60 and, we showed how as oxygen is taken up by hemoglobin that increases the affinity and makes it easier for more oxygen to bind. As oxygen is released, it makes it easier for more oxygen to be released and, oxygen leaves the hemoglobin and goes into the tissues and is released so that, it can be used by the tissues, the muscles, and so on and so forth. You can review that in Episode 60 and, in Episode 59, I gave an introduction to the respiratory system. And, the key formula we looked at (let me write that up here in red) was:
You can revisit that in Episode 59 for a review on that. This is glucose (C6H12O6), this is oxygen (6O2) then, we have carbon dioxide (6CO2) being produced and, also water (6H2O) being produced.
Now, taking this and also looking at the oxygen dissociation curve, as carbon dioxide is produced, there’s another reaction that comes into play (and I’m going to show that over here in blue), and that reaction is CO2, carbon dioxide, plus H2O, that is going to give, and this can go both ways, that’s going to give H2CO3 and then, of course, since this is water, we can end up with H+ + HCO3-:
This guy here (H2CO3) is carbonic acid, so, it’s an acid that’s why if it’s in water, it will disassociate and will get hydrogen ions (H+) and bicarbonate (HCO3-).
Now, when carbon dioxide is produced, that can cause the formation of carbonic acid and that’s going to release hydrogen ions. What is that going to do to the pH?
Well, of course, that’s going to cause the pH of the blood to decrease, so we’re going to decrease pH. I’m not going to go into too many details about what pH is but, that has to do with the acidity of the blood. If the pH goes down, it’s more acidic. If the pH goes up, it’s going to be more basic.
When the pH goes down, what that ends up doing is it reduces the affinity of hemoglobin for oxygen. So, hydrogen ions produced causes a reduction in pH, and that is going to influence the hemoglobin in such a way that the affinity for oxygen is going to be decreased and it’s going to release more oxygen than it normally would. This is called, or at least this is part of the Bohr Effect. And, I should put this with a capital ‘B’ because this is named after Christian Bohr who was the first person to describe this and, that is why we call it the Bohr effect.
So, decrease in pH decreases hemoglobin’s affinity for oxygen and, we get the Bohr effect. How that appears in the oxygen dissociation curve is that the curve actually shifts to the right. You can see this dotted red line here and, what that shows is we have a lower affinity for oxygen. So, for example, if the partial pressure of oxygen (PO2) is around 42 mmHg, normally, the hemoglobin would be approximately, what is that, 73-ish, 74-ish percent saturated with oxygen, however, because we have this Bohr effect and it shifts to the right at that same partial pressure of oxygen, we have a percent saturation of approximately 63 or 64. So, we get a 10% reduction by changing the pH by a certain amount. So, we reduce the pH, affinity for oxygen goes down, and that is called the Bohr Effect.
Now, this is one part of the equation that is a result of decreasing pH which is also a result of increasing carbon dioxide. This is a very important because, if you’re in the gym, you’re exercising, you’re working out, cellular respiration is happening even more and not only that but, if you’re exercising to the point you go into anaerobic respiration, you get lactic acid buildup and that of course is also an acid, that’s going to decrease the pH even more, decreasing the affinity for oxygen. And, you want that to be the case because this also means that more oxygen is going to be released. So, by producing more carbon dioxide because cellular respiration is happening even more, it decreases the acidity in the tissues, in the muscles, and when the blood passes there, it’s going to release more oxygen.
Now, there’s another equation that comes into play, and that also has to do with carbon dioxide. Because on the hemoglobin, you also have N-terminal amino groups (so, I’m going to write that here as) R – NH2. So, this is the N-terminal. And, in the presence of carbon dioxide (CO2), once again, that is going to cause a reaction where we are forming, and this is called carbamate (R – NH – COO-), plus H+:
So, we also have that hydrogen ion being produced here that of course, is going to decrease pH even more.
Now, what this carbonate is going to do, this is going to enhance deoxyhemoglobin stability. In other words, hemoglobin will be more stable in the deoxygenated form. In other words, it’s going to want to give up more oxygen, and of course, the hydrogen ion is also going to cause the oxygen release as we showed over here because you are decreasing pH, decreasing the affinity for oxygen. So, you can see carbon dioxide is doing this in two ways. It’s doing it by decreasing the pH; it’s doing it by producing carbamate and, that is going to enhance the deoxyhemoglobin stability. In other words, it’s more stable without oxygen so, it’s going to release oxygen, and you’re going to get this Bohr effect or the Bohr shift where the graph moves to the right, which is a good thing once again because more oxygen will be delivered to the muscles, to the tissues that need them.
That’s pretty much it! I hope that make sense with all these equations that we have here: cellular respiration, formation of bicarbonate by means of carbonic acid, and the formation of carbamates which enhances the deoxyhemoglobin stability.
That’s pretty much it for this video. As usual, if you want to see more of these kinds of videos, you can visit the website at Interactive-Biology.com. And, you’re going to get videos, quizzes and other resources to help make Biology fun. That’s it for now and, I’ll see you on the next one.