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 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 apply 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 one 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 one 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 two subunits that we refer as alpha subunits and it has two subunits that are referred to as beta subunits. So the two beta subunits are identical to each other, and the two 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 the right. And notice that it has two alpha subunits here in red and then it has two 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 want to 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 O2 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 want to 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, mb is used to represent myoglobin, whereas hb is used to represent hemoglobin. And so when mb 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 one oxygen molecule and it forms mbo2 over here and this would be referred to as the oxymyoglobin 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 O2 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.
Myoglobin vs. Hemoglobin: Study with Video Lessons, Practice Problems & Examples
Created using AIMyoglobin (Mb) is a monomeric protein with one heme group, primarily responsible for oxygen diffusion and storage in muscle tissues. In contrast, hemoglobin (Hb) is a heterotetrameric allosteric protein with four subunits (two alpha and two beta), facilitating oxygen transport in red blood cells. Both proteins exhibit reversible binding to oxygen due to their heme prosthetic groups. The dissociation equilibrium constant (Kd) and fractional saturation (θ) are crucial for understanding their protein-ligand interactions, with hemoglobin's interactions being more complex due to its multiple binding sites.
Myoglobin vs. Hemoglobin
Video transcript
Which of the following statements are true?
Myoglobin vs. Hemoglobin
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 Kd, as well as the fractional saturation, which is abbreviated as either theta or y, both apply directly to myoglobin's protein ligand interactions. 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. When we apply this 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.
Down below in our image, notice that we have it broken up based on what is review from our previous lesson videos. And then what is new here as it directly applies to myoglobin. What you'll notice is that it translates pretty much perfectly over to myoglobin, what we learned in our previous videos. Notice here what we have is the protein ligand interaction 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, O2. And then we have these set of equilibrium arrows with the rate constant, the association rate constant, lowercase Ka, 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.
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. Essentially, when we translate, this over to myoglobin, the free P and the free L are just going to be MB and O2. And then, of course, the protein ligand complex is just going to be MB2, oxygenated hemoglobin, myoglobin. Now, of course, the ratio of the rate constant is going to be the same and we also know that the Kd is the reciprocal of the Ka. And so again, this information that we learned in our previous videos applies directly. We can really do the same thing for the fractional saturation as well, where we can simply just substitute the variable. The PL here, protein ligand complex is going to be MB2. Same for down here, it's going to be MB2. 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, O2. 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 in our next practice video. So, I'll see you guys there.
If Mb's Kd = 2.5 M and the [O2] = 7.5 M, what % saturated will Mb be?
Myoglobin vs. Hemoglobin
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 myoglobin's, simply because of the fact that hemoglobin has a more complex structure. 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. Notice down below here in our image, we are showing you hemoglobin's protein ligand interaction. To generalize this and apply it to other allosteric proteins too, we're going to use the variable n here to represent the number of ligand binding sites instead of putting a 4 here for 4 oxygens. Notice here we have deoxyhemoglobin, representing our protein. There are going to be n oxygen gas molecules depending on the number of ligand binding sites. Once all those bind here to hemoglobin, we get oxyhemoglobin, which will have 4 of these oxygens bound. We will put again an n here to represent the number of ligand binding sites.
What I want you guys to recall from 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, like how we have a number here in front of this O2. We have to include these coefficients into the equilibrium constant as exponents. Recall that the dissociation equilibrium constant is an equilibrium constant itself. This means we need to include this coefficient of n here as an exponent. Anytime we have the ligand all by itself, we need to include it as an exponent. So, here where we have the KD, notice that we have the ligand all by itself. We need to include n here as the exponent. 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. 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. This is how hemoglobin's protein ligand interactions differ from myoglobin's simply by taking the coefficients of the reaction and including them as exponents.
As we move forward in our course, we'll be able to get more practice applying all these concepts, and we'll also learn more about hemoglobin and myoglobin. So I'll see you guys in our next video.
Myoglobin vs. Hemoglobin
Video transcript
In this video, we're just going to give you guys some more background information about hemoglobin. It's important to know that hemoglobin is actually found within red blood cells, and red blood cells can be abbreviated as RBC for short. The technical name is erythrocyte. Erythrocyte, red blood cell, and RBC are all synonyms. The hemoglobin molecules are found inside the red blood cells. If we take a look at our image below, it helps give us a little bit of context about where we can find these hemoglobin molecules. Here we have an image of the heme group that the hemoglobin molecule contains. Hemoglobin has four of these heme groups, which look like alien disc-shaped structures. This is going to represent the hemoglobin molecule. The hemoglobin molecules are found inside the red blood cells, which are found within the bloodstream.
To give you a bit of context on the numbers here, each individual red blood cell has approximately 270,000,000 hemoglobin molecules, which is an immense amount of hemoglobin molecules inside just one single red blood cell. Also, one drop of blood the size of a pinhead, which is very small, has about 5,000,000 red blood cells. To calculate how many hemoglobin molecules are in a drop of blood the size of a pinhead, we need to take the 5,000,000 red blood cells and multiply this by the 270,000,000 hemoglobin molecules in just one red blood cell. When we do this, the red blood cell units cancel out, and by multiplying 5,000,000 by 270,000,000, the units are in hemoglobin molecules. When we do that, what we get is a number that is incredibly massive, which is 1.35×1015 hemoglobin molecules. This number, 1.35×1015 or 1.35 quadrillion, represents the hemoglobin molecules in just one single drop of blood the size of a pinhead. This is a massive number and gives you a bit of context on how much hemoglobin is found within a red blood cell and within our bodies.
This concludes our background information of hemoglobin, and we will be able to learn a lot more about hemoglobin as we move forward in our course. See you guys in our next video.
Myoglobin vs. Hemoglobin
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 MB. Now down below in this bottom row, notice what we have is hemoglobin. And, of course, hemoglobin is abbreviated with HB. 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 going to 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.
Here’s what students ask on this topic:
What are the main differences between myoglobin and hemoglobin?
Myoglobin (Mb) is a monomeric protein with one heme group, primarily responsible for oxygen diffusion and storage in muscle tissues. Hemoglobin (Hb), on the other hand, is a heterotetrameric allosteric protein with four subunits (two alpha and two beta), facilitating oxygen transport in red blood cells. Both proteins exhibit reversible binding to oxygen due to their heme prosthetic groups. However, hemoglobin's interactions are more complex due to its multiple binding sites and allosteric regulation, which allows it to efficiently release oxygen in tissues that need it most.
Created using AIHow does the structure of hemoglobin contribute to its function?
Hemoglobin's structure, consisting of four subunits (two alpha and two beta), allows it to bind up to four oxygen molecules. This heterotetrameric structure enables cooperative binding, where the binding of one oxygen molecule increases the affinity of the remaining subunits for oxygen. This allosteric regulation is crucial for hemoglobin's function in oxygen transport, as it allows for efficient oxygen loading in the lungs and unloading in tissues. The presence of heme groups in each subunit facilitates reversible oxygen binding, essential for its role in oxygen transport.
Created using AIWhat is the role of the heme group in myoglobin and hemoglobin?
The heme group in both myoglobin and hemoglobin is essential for their ability to bind oxygen. The heme group contains an iron ion (Fe2+) that can reversibly bind to an oxygen molecule (O2). In myoglobin, there is one heme group per molecule, allowing it to bind one oxygen molecule. In hemoglobin, each of the four subunits contains a heme group, enabling it to bind up to four oxygen molecules. This reversible binding is crucial for oxygen storage in muscles (myoglobin) and oxygen transport in the blood (hemoglobin).
Created using AIWhy is hemoglobin considered an allosteric protein while myoglobin is not?
Hemoglobin is considered an allosteric protein because it has multiple subunits (four in total) that can interact with each other. This interaction allows for cooperative binding, where the binding of oxygen to one subunit increases the affinity of the remaining subunits for oxygen. This allosteric regulation is essential for hemoglobin's function in oxygen transport. In contrast, myoglobin is a monomeric protein with only one subunit, so it does not exhibit allosteric behavior. Its function is primarily to store oxygen in muscle tissues, and it binds oxygen independently without cooperative interactions.
Created using AIHow do the dissociation equilibrium constant (Kd) and fractional saturation (θ) apply to myoglobin and hemoglobin?
The dissociation equilibrium constant (Kd) and fractional saturation (θ) are crucial for understanding the protein-ligand interactions of myoglobin and hemoglobin. Kd represents the affinity of the protein for its ligand, with a lower Kd indicating higher affinity. Fractional saturation (θ) is the ratio of the concentration of ligand-bound protein to the total protein concentration. For myoglobin, which has a single binding site, these concepts are straightforward. For hemoglobin, with its multiple binding sites and cooperative binding, the calculations are more complex, involving the Hill coefficient to account for the cooperative nature of oxygen binding.
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