Erythrocytes: Hemoglobin - Video Tutorials & Practice Problems
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1
concept
Function of Hemoglobin
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7m
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In this video, we're going to talk about the function of hemoglobin. So, hemoglobin can be abbreviated as HB and it is a protein that is found inside of red blood cells or found inside of erythrocytes. And functionally its role is to transport gasses, specifically oxygen gas or 02 and carbon dioxide gas or CO2. Now, it's really important to note that inside of every red blood cell, there are tons and tons of hemoglobin protein molecules. In fact, it's estimated that just one single red blood cell contains about 250 million hemoglobin protein molecules making up about 97% of each red blood cells mass. Now, that is a ton of hemoglobin. So much so that we can pretty much think of red blood cells or erythrocytes as bags packed with tons of hemoglobin molecules. Now, the reason that hemoglobin is able to effectively transport oxygen and carbon dioxide gas is because hemoglobin is able to bind them reversibly. And so the reversible binding is incredibly important. And what it means is that not only are the hemoglobin molecules able to bind to oxygen and carbon dioxide, but they're also able to release the oxygen and carbon dioxide appropriately in the right place and the right time. And so the appropriate release of oxygen and carbon dioxide is just as critically important as the initial binding of them. And so let's take a look at our image down below where we can start to piece some things together. And so notice that this image is a bit of a silly cartoon that's designed to help you better understand the basic function of hemoglobin. And so notice that we're representing hemoglobin with these buses that you can see throughout the image. And so again, every single red blood cell would have about 250 million of these hemoglobin buses inside of them. Now notice on the left hand side, we have the lung lounge, which is supposed to represent our lungs which allows us to inhale oxygen gas and exhale carbon dioxide gas into the environment. And then on the right, what we have is the tissue tower which represents the tissues that are found throughout our body that need to be able to receive oxygen gas from the blood. Now, back to the lung lounge. Again, the lungs allow us to inhale oxygen gas. And so notice that we're showing you the oxygen gas molecules right here in the image and in the lungs is where the hemoglobin molecules can pick up or bind to those oxygen gas molecules. And so what we can say is that 02 pickup or oxygen gas pickup occurs in the lungs. And so notice again, the hemoglobin molecule is being shown as this bus. And what you'll notice is that this is a four seater bus that is binding to four oxygen gas molecules. And so this has to do with the structure of the hemoglobin molecule, which we'll talk more about in our next lesson video. But for now, you should think of the hemoglobin molecule as a four seater bus because each hemoglobin molecule combined to four oxygen gas molecules. And so the hemoglobin again is able to effectively transport the oxygen because it can reversibly bind to the oxygen, it can bind to oxygen and pick it up in the lungs. But when the blood is pumped to the tissues, the conditions change in the tissues so that the hemoglobin will actually release or drop off the oxygen. And so we have 02 drop off in the tissue tower. And so the oxygen that is dropped off to the tissues can then be utilized by those tissues to drive their metabolism and uh through the metabolism of the tissues, they will also create waste products uh such as carbon dioxide gas. And so notice that we have carbon dioxide gas being shown below here. And after the hemoglobin has dropped off the oxygen gas, it can then pick up the carbon dioxide gas waste product. And so notice that we have CO2 pick up in the tissue tower. And so you can see here that the CO2 molecules are bound to the hemoglobin. But notice that the CO2 molecules are bound in a different position than what we saw, the oxygen gas molecules were bound up above. And the reason for this again has to do with the structure of the hemoglobin and the nature of how it goes about binding to oxygen versus how it goes about binding to carbon dioxide. And again, we'll talk more about this in our next lesson video. But for now, what you should note is that the CO2 molecules will bind to hemoglobin but at a different position than it will bind to the oxygen gas. But regardless, the hemoglobin can still affect transport the carbon dioxide gas because again, it can bind to them in the tissues. But when it gets to the lungs, it can enco it will encounter different a different set of conditions that will allow it to drop off and release the carbon dioxide gas. And so notice we have CO2 drop off in the lungs and that allows the lungs to exhale the carbon dioxide. And then when we inhale again, we can inhale more oxygen gas so that this entire cycle can repeat over and over and over again. Now, something very important that you should know is that although hemoglobin does transport both oxygen and carbon dioxide gas, hemoglobin actually plays a larger role in transporting oxygen gas and a smaller role in transporting carbon dioxide gas. And the reason for that is because hemoglobin only transports a small frame action of the total amount of carbon dioxide gas. And most of the carbon dioxide gas is actually transported by the blood's plasma, not by hemoglobin. And this is an idea that we'll get to talk more about as we move forward. And so the last thing that I'll leave you off with is notice we're using this reddish color to represent the oxygenated blood where hemoglobin is bound to oxygen. And notice we're using this bluish color to represent the deoxygenated blood where hemoglobin is bound to carbon dioxide instead of oxygen. And so these colors are pretty consistently used moving forward in our video lessons, but also in sources outside of our video lessons like textbooks, for example. And the reason these colors are used are only to help visually distinguish the two types of blood and to help enhance student learning. However, it's important to note that blood is never actually a blue color. When hemoglobin is bound to oxygen, it is going to make the blood a bright red color. But when hemoglobin is bound to carbon dioxide, it's not actually a blue color, instead, it's a dark red color. And so again, blood is always going to be red, but the shading of that red will vary depending on the oxygen content of the blood, brighter red when it has high oxygen content and darker red when it has low oxygen content. And so again, that's important to keep in mind that being said, this year concludes our video lesson on the function of hemoglobin. And moving forward, we'll get to learn more and talk about the structure of hemoglobin. So I'll see you all in our next video.
2
example
Erythrocytes: Hemoglobin Example 1
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1m
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So here we have an example problem that's asking which of the following is most likely to occur if hemoglobin started binding to oxygen irreversibly. And we've got these four potential answer options down below. And so first, we need to recall from our previous lesson video that hemoglobin actually binds to oxygen reversibly, not irreversibly. And so this problem is really just an if scenario. And so recall that the reversible binding means that hemoglobin can not only bind to oxygen, but it can also release oxygen appropriately. And so what this means is the reversible binding allows hemoglobin to bind and release oxygen appropriately in the right place at the right time. And ultimately, this is what allows hemoglobin to serve as an efficient transporter of oxygen and deliver oxygen to the tissues. Now, irreversible binding would mean that hemoglobin would bind to oxygen, but it would not release the oxygen. And if it didn't release the oxygen, it would not be able to deliver the oxygen to the tissues and therefore the tissues would receive less oxygen. And so notice answer option c says your tissues would receive less oxygen. And so this is actually the correct answer to this problem. And so we can indicate C is the correct answer. Now, the oxygenation status of the blood does not directly impact the speed at which the blood travels through the body. And so option A which says your blood would circulate through your body slower. And option B which says your blood would circulate through your body faster are both going to be incorrect. And then option D says your tissues would receive more oxygen, which is the exact opposite of what would happen with irreversible binding. And so we can eliminate option D. And so again, see here is the correct answer to this example that concludes this example and I'll see you all in our next video.
3
Problem
Problem
Why is it important for erythrocytes to have a high surface area to volume ratio?
A
Increased cell flexibility.
B
Allows for more efficient gas exchange.
C
Allows each RBC to carry more hemoglobin.
D
Allows RBCs to ft through small gaps.
4
concept
Structure of Hemoglobin
Video duration:
6m
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In this video, we're going to talk about the structure of hemoglobin. And so we already know from our last lesson video that hemoglobin is a molecule found inside of red blood cells or inside of erythrocytes. And it's found in very large numbers. And functionally, we already know hemoglobin is important for the transport of oxygen and carbon dioxide gasses. Although recall, hemoglobin plays a larger role in the transport of oxygen gas since most carbon dioxide gas is transported by the blood's plasma, not by hemoglobin. Now, structurally hemoglobin, which again can be abbreviated as HB is a four subunit protein, which means that it has four separate protein chains that come together to form the complete hemoglobin molecule. And this four subunit protein is called globin. Now, this four subunit protein globin specifically transports oxygen gas using what are known as heme groups. And so we'll be able to see this down below in our image. But really this is where hemoglobin gets its name from, from the presence of the heme groups and the presence of this force of unit protein globin. Now, what's really important to note is that each of the four subunits in the hemoglobin molecule is going to have its own heme group. And so there are four heme groups, one for each of the four subunits of the hemoglobin molecule. And each heme group has its own central iron atom or its own central fe two plus atom. And each iron atom is capable of reversibly binding just one oxygen gas molecule. And so, when hemoglobin binds to oxygen gas, in this way, we refer to it as oxyhemoglobin. And so once again, because there are four subunits in one hemoglobin molecule, each with their own heme group and each capable of binding one oxygen gas molecule. What this means is that each hemoglobin molecule can actually carry up to a maximum of four oxygen gas molecules at once again, since each oxygen, each subunit can carry one oxygen gas molecule. And so we can actually indicate this with this chemical formula that you see right here where again, the HB is the abbreviation for hemoglobin. The 02 is the chemical formula for oxygen gas. And then the four subscript here is indicating that there are four oxygen gas molecules bound to this one hemoglobin, which has four subunits. And so this detail here is very important to keep in mind that each hemoglobin can bind up to a maximum of four oxygen gas molecules. Now, again, we know hemoglobin can also bind and transport carbon dioxide gas. And so it turns out that hemoglobin can also bind up to four carbon dioxide gas molecules at once. And when hemoglobin is bound to carbon dioxide gas, we specifically refer to it as deoxy hemoglobin or carbaminohemoglobin. Uh But what's really important to note is that hemoglobin will bind oxygen and carbon dioxide via different mechanisms. Once again, hemoglobin will bind to oxygen gas using heme groups. But the heme groups do not bind to carbon dioxide gas. Instead, the carbon dioxide gas is going to be bound via amino groups, not the heme group. So let's take a look at our image down below to get a better understanding. And notice on the left hand side, we're showing you the same exact buses that we showed you in our last lesson video which represent hemoglobin and notice that this red bus at the top is bound to four oxygen gas molecules. And so the red bus represents oxyhemoglobin and the blue bus down below notice is bound to four carbon dioxide gas molecules. And so the blue bus represents D oxy hemoglobin or carb amino hemoglobin. Now, one thing to notice is that the deoxy hemoglobin is binding to the carbon dioxide gas at a different position than the oxyhemoglobin binds to the oxygen gas. And so this is supposed to represent that hemoglobin will bind to oxygen and carbon dioxide via different mechanisms. Now, on the right, we're focusing in on hemoglobin structure and we know once again that hemoglobin is a four subunit protein. In fact, hemoglobin has two subunits shown here in blue, which are alpha subunits. And the alpha can actually be written out as alpha or symbolized with the Greek letter alpha. And then it has these two beta subunits. And again, it can be written out as beta or symbolized with the Greek letter beta. And so the two alpha subunits are identical to each other and the two beta subunits are identical to each other. But of course, the alpha and beta subunits are different from one another. But regardless all four of these sub units, which you'll notice has a heme group that is present. And so notice on the right, we are zooming in to the structure of the heme group. And so it does have a pretty complex structure. And uh in most cases, you wouldn't be expected to have to memorize the structure. Uh But this structure here is the heme group. So we can go ahead and label it as so. And what you'll notice is that right in the center of the heme group uh is going to be that iron atom, the fe two plus atom. And so this iron atom is what is capable of reversibly binding oxygen gas. And so, although it's not being shown, again, it's important to know that the iron interacts with the oxygen gas for binding. And so again, because each of these subunits has a heme group that allows each one of these sub units to reversibly bind one oxygen. And that means that this entire hemoglobin molecule can bind a maximum of four oxygen gas molecules as we discussed. And so this year concludes our brief lesson on the structure of hemoglobin. And as we move forward, we'll be able to apply these concepts and learn more. So I'll see you all in our next video.
5
example
Erythrocytes: Hemoglobin Example 2
Video duration:
2m
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So here we have an example problem that's asking if each erythrocyte or red blood cell can carry 250 million hemoglobin molecules. How many molecules of oxygen gas can each erythrocyte carry at a time? And we've got these four potential answer options down below. And so to solve this problem, we'll need to do just a little bit of math. And so again, the problem is telling us that there are 250 million hemoglobin molecules which we can abbreviate as HP for every one erythrocyte or for every one red blood cell, which we can abbreviate as RVC. And we need to recall from our previous lesson videos that for every one hemoglobin molecule, it can carry up to a maximum of four oxygen gas molecules. And so really what we need to do is multiply these two ratios together. And so this becomes a very simple multiplication problem. And so what you'll notice is that the units of hemoglobin are going to cancel each other out, so we can cross those off. And what we're left with are units of oxygen and units of red blood cells. And so we can go ahead and have our ratio here and add in those units of oxygen and again, red blood cell on bottom. And so all we need to do is multiply our numbers straight across in these ratios. So 250 million times four is actually 1 billion. And so we can put 1 billion on top and then of course, one times one is going to be one and so we can put one down below. And so this is going to be our answer over here that there are going to be 1 billion oxygen gas molecules for every one red blood cell. And that's exactly what the problem is asking us. And so notice that answer option D over here says 1 billion. And that is going to be the correct answer for this problem. Theoretically, if every red blood cell carried 250 million hemoglobin molecules, then theoretically each erythrocyte could carry up to a maximum of 1 billion oxygen gas molecules. So this year concludes this problem and I'll see you all in our next video.
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Problem
Problem
How many heme groups are required to synthesize 4 hemoglobin molecules?
A
4
B
8
C
16
D
32
7
Problem
Problem
Cynthia lives in Miami, a city at low altitude. She goes on a month-long trip to the Andes Mountain range (at high altitude) where the air pressure is lower and therefore there is less oxygen in each breath she takes. Upon returning to Miami, how might a sample of her blood differ from a sample taken before she left for her trip?
A
Each of her blood cells would carry fewer hemoglobin molecules.
B
Each of her hemoglobin molecules would carry 5-6 oxygen molecules.
C
Her hematocrit will have increased (more erythrocytes per μL).
D
There would likely be no change.
8
Problem
Problem
Anemia is a blood disorder where the O2-carrying capacity of blood is too low to support the body's tissues. Which of the following is not a possible cause of anemia?
A
Iron deficiency.
B
Blood loss.
C
Deformed hemoglobin.
D
Excess erythrocytes.
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