Myoglobin vs. Hemoglobin - Video Tutorials & Practice Problems
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Myoglobin vs. Hemoglobin
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8m
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Video transcript
In this video, we're going to formally introduce myoglobin and hemoglobin. So as you guys may already know, both myoglobin and hemoglobin are proteins that are respectively abbreviated with mb and hb. And so moving forward in our course, we're going to use mb and hb a lot to abbreviate myoglobin and hemoglobin. Now, the reason that your professors and your textbooks like to focus so much on myoglobin and hemoglobin is because both of these proteins are very well studied proteins whose functions and characteristics have been very well characterized. And not only that, both myoglobin and hemoglobin are great examples for many of the protein and enzyme concepts that we learned about in our previous lesson videos. And so here, we're we're going to be applying a lot of those older concepts directly to myoglobin and hemoglobin. Now technically, myoglobin and hemoglobin are not enzymes, And that's because they do not catalyze a reaction and convert substrate into product. However, myoglobin and hemoglobin do bind to a ligand. So, protein ligand interactions applies directly to both myoglobin and hemoglobin. Also, it's important to note that allosteric regulation does not only apply to enzymes. It can also apply to proteins that participate in protein ligand interactions. Now, myoglobin, as you guys may already know, is a monomeric protein. Meaning that it only has 1 protein subunit. Mono means 1. And so if we take a look at our image down below on the left hand side over here, notice that we have this brown structure here, and this brown structure only shows 1 subunit, one chain and this is representing myoglobin's structure. Oxygen diffusion, storage, and supply to muscle tissues and vertebrates. Now, hemoglobin on the other hand is a heterotetrameric allosteric protein and that's a handful but really if we break it down, it's not very complicated at all. So tetra is a prefix that means 4. And so essentially, what this is saying is that hemoglobin has 4 different polypeptide chains, 4 different subunits. And then the hetero here, of course, just means different, meaning that not all 4 of these subunits are exactly the same. They're going to be somewhat different. And in fact, if we break down these 4 subunits that are found in hemoglobin structure, we'll see that it actually has 2 subunits that we refer as alpha subunits and it has 2 subunits that are referred to as beta subunits. So the 2 beta subunits are identical to each other, and the 2 alpha subunits are identical to each other, but, obviously the alpha and beta subunits will be different, and that's why we refer to it as hetero. And so, really, hemoglobin, its function is to circulate and transport oxygen via the blood. And so if we take a look at our image down below, notice that we have hemoglobin structure over here on on the right. And notice that it has 2 alpha subunits here in red and then it has 2 beta subunits here in blue. And so, you can see that hemoglobin is indeed a heterotetrameric protein. And not only is it a heterotetrameric protein, but again, I wanna emphasize that it's also an allosteric protein, meaning that all of the allosteric concepts that we learned about in our previous lesson videos also apply to Hemoglobin And we'll be able to focus more on those allosteric concepts of hemoglobin a little bit later in our course. Now, what's important to note is that both of these proteins, hemoglobin and myoglobin, are capable of reversibly binding to oxygen gas. Which we're going to abbreviate as just o 2 moving forward in our course because that's the molecular structure. And so, the reason that both of these enzymes are capable of reversibly binding oxygen gas is because both of them have what's known as a heme prosthetic group. And so, notice that myoglobin's heme prosthetic group is represented by this little alien disc structure that we see right here. And so, it turns out that myoglobin's structure only has one heme group for its one subunit. However, if we look at hemoglobin structure over here on the right, notice that it actually has 4 of these heme groups And so it has one heme group per subunit. So, it turns out hemoglobin, has more heme groups than myoglobin, but, they both do indeed have heme groups. And, it's the heme group that allows both of these proteins to bind oxygen. Now, again, I really wanna emphasize the fact that although myoglobin and hemoglobin need to be able to bind oxygen, it's also equally as important for them to be able to release oxygen when the time is right. And so really this is what we're referring to as reversible binding of oxygen. Not only do they need to be able to bind oxygen, but they need to be able to release the oxygen as well. And so, we'll talk more about this reversible binding of both of these proteins later in our course. Now, down below, notice that for myoglobin over here on the left, we're emphasizing the fact that its function is for oxygen diffusion and storage, specifically in muscle tissues like this bicep here that we see. And, hemoglobin on the other hand, which we have over here on the right, its function is for oxygen circulation and transport, specifically in the blood. And so here you can see that we're zooming in on the blood stream and so hemoglobin, as we'll note more about later, is actually found inside of the red blood cells that we see here. Now, over here on the right, what we have is a more chemical version to represent myoglobin and hemoglobin. And, again, remember, m b is used to represent myoglobin, whereas h b is used to represent hemoglobin. And so when m b is written in this form here, it's usually referred to as deoxymyoglobin because it's not attached to the oxygen molecule just yet. And the same goes for hemoglobin. When it's just written as HB, it's the deoxyhemoglobin form. And so, notice that myoglobin, because it only has one of these heme groups, it's only capable of binding 1 oxygen molecule and it forms m b o two over here and this would be referred to as the oxymoglobin because it's now been oxygenated. Whereas, hemoglobin down here below, notice that it can actually bind to 4 oxygen molecules and that's because it has 4 of these heme groups. And so, when hemoglobin binds these 4 oxygen molecules, its chemical formula turns to this format here where it has 4 of these O 2 molecules bound. And so this is the oxyhemoglobin format. And so, this here concludes our introduction to myoglobin and hemoglobin and we'll be able to continue to learn a lot more about both of these proteins as we move forward in our course. So I'll see you guys in our next video
2
Problem
Problem
Which of the following statements are true?
A
Both myoglobin and hemoglobin irreversibly bind oxygen gas (O2).
B
Myoglobin has a single subunit, whereas hemoglobin has four identical subunits.
C
Hemoglobin and myoglobin each contain a single heme group.
D
Each individual subunit of hemoglobin contains a heme group.
E
Hemoglobin transports, stores and supplies oxygen in the muscle tissue.
F
A and B.
G
A and C.
H
B and C.
3
concept
Myoglobin vs. Hemoglobin
Video duration:
4m
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Video transcript
In this video, we're going to talk about myoglobin's protein ligand interactions. And so protein ligand affinity, which is most commonly represented by the dissociation equilibrium constant, capital k d, as well as the fractional saturation, which is abbreviated as either theta or y, both apply directly to myoglobin's protein ligand interactions. And so recall from our previous lesson videos that the fractional saturation, theta or y, is really just a ratio. It's the ratio of the proteins bound by ligand over the total concentration of protein. And so, when we apply this specifically to myoglobin, we can specifically to myoglobin, we can say that the fractional saturation of myoglobin is just the ratio oxygenated protein, which would be the protein ligand complex, over total protein, which again is, the protein bound by ligand as well as the protein not bound by ligand. And so, down below in our image, notice that we have it broken up based off of what is review from our previous lesson videos. And then what is new here as it directly applies to myoglobin. And so, what you'll notice is that it translates pretty much perfectly over to myoglobin, what we learned in our previous videos. And so notice here what we have is the protein ligand interaction myoglobin, specifically the deoxy form of myoglobin. Myoglobin, specifically the deoxy form of myoglobin. Then we have, the ligand is next, and, of course, the ligand for myoglobin is going to be the oxygen gas molecule, o 2. And then we have these set of equilibrium arrows with the rate constant, the association rate constant, lowercase k a, and the dissociation rate constant, lowercase kd. And, of course, the protein ligand complex is going to be myoglobin in its oxygenated form, so oxymyoglobin. So pretty easy. It translates directly over to myoglobin. Now, the same goes for the kd as well, the dissociation equilibrium constant, which is, of course, going to be the ratio of the products over the reactant. And, of course, for the dissociation going backwards, the product is going to be p and l, free p and l. And so, essentially, when we translate, this over to myoglobin, the free p and the free l are just gonna be m b and o 2. So we can add that in here, m b and o 2. And And then, of course, the protein ligand complex is just going to be mb02, oxygenated hemoglobin, myoglobin. Now, of course, the ratio of the rate constant is gonna be the same and, of course, we also know that the k d is the reciprocal of the k a. And so again, this information that we learned in our previous videos applies directly. And we can really do the same thing for the fractional saturation as well, where we can simply just substitute the variable. So, of course, the PL here, protein ligand complex is gonna be mb02. Same for down here, it's going to be mb02. And then, of course, the free protein right here is just going to be myoglobin. And then of course the ligand for myoglobin is going to be oxygen, o 2, And, here we also have oxygen. And so, essentially, what we're doing is we're taking everything that we learned from our previous lesson videos and we're applying it directly to Myoglobin. And so we can get some practice utilizing, this new application of our previous concepts to in our next practice video. So, I'll see you guys there.
4
Problem
Problem
If Mb's Kd = 2.5 M and the [O2] = 7.5 M, what % saturated will Mb be?
A
12%
B
75%
C
0.75%
D
64%
5
concept
Myoglobin vs. Hemoglobin
Video duration:
3m
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Video transcript
So now that we've covered myoglobin's protein ligand interactions, in this video we're going to focus on hemoglobin's protein ligand interactions, which are actually just a bit more complicated than myoglobins, simply because of the fact that hemoglobin has a more complex structure. And so recall that myoglobin is not an allosteric protein because it only has one single subunit. Whereas hemoglobin on the other hand is an allosteric protein with multiple subunits, each of which can bind a ligand of oxygen. And so notice down below here in our image, we are showing you hemoglobin's protein ligand interaction. And so just to be able to generalize this and apply this to other allosteric proteins too, we're gonna use the variable n here to represent the number of ligand binding sites instead of putting a 4 here for 4 oxygens. And so, notice here we have deoxyhemoglobin, and that is representing our protein. And so, the oxygen gas molecule, there's going to be an n number of oxygen gas molecules depending on the number of ligand binding sites. And so here we have 4 oxygen gas molecules that we can see. And once all of those bind here to hemoglobin, we can get oxyhemoglobin. And so, it will have 4 of these, oxygens bound once all of them are bound. And so we will put again an n here to represent the number of ligand binding sites. And so what I want you guys to recall from way way back in our older lesson videos is that whenever we have coefficients in a reaction, and recall that coefficients are just numbers in front of a molecule, kind of like how we have a number here in front of this O two. We have to include these coefficients into the equilibrium constant as exponents. And so, recall that literally the, dissociation equilibrium constant is an equilibrium constant itself. And so what means is we need to be able to include this coefficient of n here as an exponent. And so anytime we have the ligand all by itself, we need to include it as an exponent. And so, here where we have the KD, notice that we have the ligand all by itself. So we need to include n here as the exponent. And then, of course, now our protein ligand complex has changed in a way where it has the n here as the, subscript, so we need to include that as well. And so, here over here for the fractional saturation, we can include n here and the protein ligand complex as the subscript. And of course, for the ligand all by itself, it will be included as an exponent here. And so really, this is how, hemoglobin's protein ligand interactions, differ from myoglobin simply by taking the coefficients of the reaction and including them as exponents. And, really, that's the main difference. And so, as we move forward in our course, we'll be able to get more and more practice applying all these concepts and we'll also learn more and more about hemoglobin and myoglobin. So I'll see you guys in our next video.
6
concept
Myoglobin vs. Hemoglobin
Video duration:
3m
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Video transcript
In this video, we're just gonna give you guys some more background information about hemoglobin. And so it's important to know that hemoglobin is actually found with within red blood cells, and red blood cells can be abbreviated with RBC for short. And the technical name is erythrocyte. And so erythrocyte and red blood cell, as well as RBC, are all synonyms of one another. And so again, the hemoglobin molecules are found inside of the red blood cells. And so, if we take a look down below at our image down below, it helps give us a little bit of context of where we can find these hemoglobin molecules. So, over here, what we have is an image of the heme group that we know the hemoglobin molecule contains. And so we know that hemoglobin has 4 of these heme groups that really look like alien disc shaped, structures. And so, of course, this is going to represent the hemoglobin molecule. Now, again, the hemoglobin molecules are found inside of the red blood cells. So, they're gonna be found on the inside of these erythrocytes, which again is a synonym for red blood cells. And then, of course, inside, these red blood cells are going to be found within the blood stream. And, basically, to give you guys a little bit of context on the numbers here, so, each individual red blood cell has approximately 270,000,000 molecules of hemoglobin, and that is an immense amount of hemoglobin molecules inside of just one single red blood cell. Now, also, one drop of blood the size of a pinhead, which is very, very small, has about 5,000,000 red blood cells. And so if we were to calculate how many hemoglobin molecules are in a drop of blood the size of a pinhead, all we would need to do is take the 5,000,000 red blood cells, so the 5,000,000 red blood cells and multiply this, by the 270,000,000 so the 270,000,000 hemoglobin molecules, and just one red blood cell. And so when we do this, we get the red blood cell units to cancel out. And, we can take this 5,000,000 and multiply it by 270,000,000 and the units are gonna be in hemoglobin. And when we do that, what we get is a number that is incredibly massive that I'll write down here. And it is 1.35 times 10 to the 15th hemoglobin molecules. And so this number here is actually 1 point 35 quadrillion hemoglobin molecules and just, one single drop of blood the size of a pinhead. So this is a massive, massive number, and that just gives you guys a little bit of context of, how much hemoglobin is found within a red blood cell and within our bodies. And so, this here, concludes our background information of hemoglobin and we'll, again, we'll be able to learn a lot more about hemoglobin as we move forward in our course. So see you guys in our next video.
7
concept
Myoglobin vs. Hemoglobin
Video duration:
2m
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Video transcript
In this video, we're going to do a quick recap of some of the similarities and differences between myoglobin and hemoglobin. And so we're going to fill out this table down below and notice that in this first row right here, what we have is myoglobin. And, of course, myoglobin is abbreviated with m b. Now down below in this bottom row, notice what we have is hemoglobin. And, of course, hemoglobin is abbreviated with h b. Now, in order to fill out this first row right here, what we need to figure out is the number of subunits and recall that myoglobin only has one single polypeptide chain, which means that myoglobin only has one single subunit. And because it only has one single subunit, myoglobin is not an allosteric protein. Whereas, hemoglobin on the other hand, notice has 4 separate polypeptide chains, which means that hemoglobin has 4 subunits. And hemoglobin has 2 alpha subunits and 2 beta subunits. And that's what composes these 4 subunits. And also recall that hemoglobin is an allosteric protein. Now in terms of the number of heme groups, we can visually see that myoglobin only has one heme group which is this alien disc shaped structure right here, this UFO structure, And, because it only has one heme group, we can put one over here. So it has one heme group for its one subunit, and, of course, hemoglobin, on the other hand, actually has 4 heme groups, one for each of its 4 subunits. And so, we can put over here that it also has 4 heme groups. Now myoglobin is going to be located specifically in muscle tissues, and we'll talk more about this idea later in our course. Whereas, hemoglobin on the other hand, we said in our previous lesson video is gonna be found within red blood cells in the bloodstream. So I'll abbreviate red blood cells with RBCs. And then, of course, in terms of reversibly binding oxygen, both myoglobin and hemoglobin can reversibly bind oxygen, and that's because they both have heme groups. And, really, it's these heme groups that are responsible for the ability to reversibly bind oxygen. And because, again, both myoglobin and hemoglobin have heme groups, they can both reversibly bind oxygen. And we'll be able to talk more about this ability to bind, reversibly bind oxygen, later in our course. But for now, this concludes the recap of myoglobin versus hemoglobin and I'll see you guys in our next video.