Hemoglobin Carbonation & Protonation - Video Tutorials & Practice Problems
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Hemoglobin Carbonation & Protonation
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Video transcript
In this video, we're going to begin our discussion on hemoglobin carbonation and protonation. So at this point in our course, we already know that hemoglobin can bind to to carbon dioxide via carbonation and it can also bind to protons via protonation. Now in this video, we're mainly going to talk about hemoglobin carbonation, but in our next video, we'll talk about hemoglobin protonation. Now most of the information in this video is actually going to be review from our previous lesson videos, but we are going to reveal some critical information about hemoglobin carbonation that you guys should be familiar with. So we already know that hemoglobin carbonation can be referred to as just hbco2, and hemoglobin carbonation occurs mainly in the tissues, not in the lungs. Now this allows hemoglobin to directly transport some small amount, about 10% of the carbon dioxide from the tissues to the lungs. Now this next bullet point here is going to reveal the critical information that we need to know about hemoglobin carbonation. And so at this point, we know that hemoglobin has 4 separate subunits. And so each of hemoglobin's 4 separate subunits can actually bind to a carbon dioxide molecule, forming a carbamate group on each of the free alpha amino groups on each of hemoglobin subunits to form what we call carbaminohemoglobin, which is just hemoglobin, with carbamate groups bound. And again, this is what we're going to refer to as hbco 2. And so if we take a look at our image down below, notice we're showing you the formation of carbaminohemoglobin. And notice that this molecule over here on the far left is our c o two molecule, our carbon dioxide molecule. And then in red right here, what we have is hemoglobins and terminal amino acid residue. Essentially, the free alpha amino group is right here at this position. And so notice that this reaction right here will release a proton, and in the meantime, it forms the carbaminohemoglobin. And so this is going to have just a carbon dioxide molecule attached as a carboxylate group, and together, this carboxylate group attached to this nitrogen here forms the carbamate group. And, together, this entire thing is referred to as carbaminohemoglobin, h b c o 2. And what's important to note is that, again, this is just showing the reaction for just one of the subunits of hemoglobin, interacting with c o two. However, remember that each of hemoglobin subunits can undergo this reaction. And so what this means is that if we consider the hemoglobin, 4 subunits, each of the 4 subunits combined, a c02 molecule. And so 4 c 02 molecules can be transported by 1 hemoglobin. And so, recall from our previous lesson videos that hemoglobin carbonation stabilizes the t state, which is the tense state and binds ligand or oxygen inefficiently. And so if we stabilize the t state, that's going to cause the release of oxygen. And so notice over here on the left where hemoglobin is carbonated, it's present in the t state. And notice it's not bound to any oxygen. And so, the reason for this is because in the tissues, there's such a high partial pressure of carbon dioxide, lots of carbon dioxide being produced in the tissues. And so there's so much carbon dioxide that hemoglobin is bound to bind to some of that carbon dioxide. So hemoglobin gets carbonated at these high partial pressures, and, of course, that stabilizes the t state and causes the release of oxygen. And so that's why we can see over here, we have the t state of hemoglobin in the tissue. So here, we have a bicep to represent the tissues. And, again, this has to do with the high partial pressure of carbon dioxide in the tissues so high that hemoglobin is bound to bind to some of that c o two. Now in the lungs, there's the complete opposite condition of low partial pressure of c o two in the lungs because, we're constantly exhaling c o two. And so because we're breathing out all of that c o 2, hemoglobin is going to be decarbonated, essentially releasing the c o 2 so that it can be exhaled as well. And now the hemoglobin molecule is going to be in the r state when it's in the lungs. And, again, this has to do with the low partial pressure of CO 2 in the lungs. And so, basically, the main takeaway here is that hemoglobin carbonation occurs only in the tissues as we can see over here. And, essentially, carbaminohemoglobin is just referring to hemoglobin that's bound to c o 2 molecules. So this here concludes our lesson on hemoglobin carbonation. We'll be able to get a little bit practice in our next video, and then we'll move on to hemoglobin protonation. So I'll see you guys in our next video.
2
Problem
Problem
Which option best corresponds with the effect of CO2 on hemoglobin's O2-binding?
A
Hb's O2-affinity decreases with lower CO2 concentration.
B
Hb's O2-affinity increases with higher CO2 concentration.
C
Low pCO2 stabilizes the T state conformation of Hemoglobin.
D
High pCO2 stabilizes the R state conformation of Hemoglobin.
E
High pCO2 stabilizes the T state conformation of Hemoglobin.
3
concept
Hemoglobin Carbonation & Protonation
Video duration:
3m
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Video transcript
So now that we've covered hemoglobin carbonation, in this video we're going to focus on hemoglobin protonation, which we already know from our previous lesson videos can be abbreviated as just h h b plus. And so just like hemoglobin carbonation, hemoglobin protonation occurs only in the tissues, not in the lungs. And so what's important to note about hemoglobin protonation is that hemoglobin can actually become protonated on several amino acid r groups in order to carry h plus as h h b plus. And because it's actually these r groups that are susceptible to protonation, this means that there are more protonation sites than there are carbonation sites. And so recall in our previous lesson video when we talked about hemoglobin carbonation, we said that it's only the free alpha amino groups that can be carbonated, and there are only 4 free alpha amino groups, so there are only 4 carbonation sites. However, here with hemoglobin protein, again, it's the r groups that are being protonated. And so there are several amino acid r groups that can be protonated in hemoglobin structure. And so notice down below, here we're showing hemoglobin structure being protonated, and notice that there are way more protonation sites sites than there are carbonation sites. And so what's important to know is that in the relatively high concentration of hydrogen ions or low pH of the tissues, there are so much hydrogen ion concentration that hemoglobin is bound to grab onto one of those hydrogen ions and become protonated to form HHB plus. And, of course, that's going to stabilize the t state and release oxygen. And so if we take a look down below, notice that when hemoglobin is protonated as HHB plus, it's going to be stabilizing the t state. It's going to be releasing oxygen, and this is all due to the low pH in the tissues or the high hydrogen ion ion concentration in the muscle tissues. Now in the lungs, we have the complete opposite, concentration of hydrogen ion. So we have very, very low concentration of hydrogen ion or a high pH in the lungs, and there's such a low concentration of hydrogen plus. And, of course, when it releases h plus, it can then bind to all of the oxygen that's present in the lungs, and so that allows it to bind oxygen in the r state. And again, this is due to the low I'm sorry, the high, pH in the lungs and the low concentration of hydrogen ion. Hemoglobin protonation, specifically in the tissues. And again, that is really the main takeaway here that hemoglobin protonation as well as hemoglobin carbonation, both occur in the tissues and not in the lungs. And so, I'll see you guys in our next video where we'll be able to apply some of these concepts.
4
Problem
Problem
Which statement is true about protons binding to hemoglobin?
A
Protons stabilize the T-state increasing the affinity of hemoglobin for oxygen.
B
Protons stabilize the T-state decreasing the affinity of hemoglobin for oxygen.
C
Protons stabilize the R-state increasing the affinity of hemoglobin for oxygen.
D
Protons stabilize the R-state decreasing the affinity of hemoglobin for oxygen.
5
concept
Hemoglobin Carbonation & Protonation
Video duration:
1m
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Video transcript
In this video, we're going to do a quick recap on hemoglobin carbonation and protonation. And so notice looking down below at our image on the left hand side over here, we're zooming in specifically into the bloodstream by the tissues. And so notice that in the tissues, we have a very, very high high concentration of c o two, which is going to lead to a high concentration of h plus in the tissues. And so there's so much c o two and so much h+in the tissues that hemoglobin is bound to bind to the h+c02. And of course, when it binds to the h+c0 2, it's going to be in its t state and release oxygen. And then, of course, myoglobin can facilitate the oxygen to diffusion into the tissues. Now in the lungs, on the other hand, notice that there's the exact opposite conditions as the tissue. So there's a very, very low concentration of c02, and, of course, the low concentration of c02 translates to the inside of the red blood cell. And the low c02 causes these equilibriums here to shift to the right to compensate, and that's going to decrease the concentration of hydrogen ion. So we have a low concentration of c o two and a low concentration of hydrogen ion. And so it's so low that hemoglobin is bound to release some of its hydrogen ion so that it can also participate in this shift to the right, and it can release its c o two so that it can also be breathed out of the cell. And so, of course, when it releases the h+c02, it can also bind to the very, very high concentration of oxygen that's constantly being breathed in. And so hemoglobin is going to bind the oxygen, release the h+ and c02, and be present in its r state when it's in the lungs. And so this here is our brief recap on hemoglobin carbonation and protonation. And again, we'll be able to talk more about these ideas as we move forward in our course. So I'll see you guys in our next video.
6
Problem
Problem
Alkalemia is a disease associated with an abnormal increase in the pH of a patient's blood due to rapid breathing (hyperventilation). How would alkalemia affect the oxygen binding affinity of the patient's hemoglobin?
A
P50 and oxygen affinity decrease.
B
P50 and oxygen affinity increase.
C
P50 decreases and oxygen affinity increases.
D
P50 increases and oxygen affinity decreases.
E
P50 and oxygen affinity remain the same.
7
Problem
Problem
Choose all of the following molecules that, when bound, trigger hemoglobin's transition from T to R state.