June 7, 2011

060 Hemoglobin and the Oxygen-Dissociation Curve

Ever wonder how the oxygen binds to our blood cells and sent to the different parts of our body? Watch and learn with Leslie as he explains how this happens and uses the Oxygen-Dissociation Curve to describe this event.

Have fun!

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 60, I’m going to be talking about hemoglobin and what’s called the oxygen-dissociation curve. So, let’s get right into it.

We’ve already done an introduction to the respiratory system and we’ve shown how the heart beats and sends the blood. When the right ventricle sends the blood, it sends it to the lungs that comes back to the left atria and then, the left ventricle pumps and that sends the blood through the rest of the body.

We’ve also looked in the lungs and seen how we have the trachea going into the bronchi and then that splits off into the bronchioles, and as you can see here, that gives us the alveoli and it’s in the alveoli where we have the exchange between the oxygen coming into the bloodstream, via the capillaries that we have here, and the carbon dioxide leaving the capillaries going into the lungs and being sent from the body.

Now, when the blood comes in here, it is picking up oxygen, and the type of blood cells that are picking up the oxygen, would be the red blood cells. Here you can see a picture of a few red blood cells, of course, it’s simplified. It’s not showing the white blood cells or anything else. It’s just showing the red blood cells and these are the blood cells that pick up that oxygen.

In the red blood cells, we have special molecule. That molecule is called hemoglobin. You can see a three-dimensional image here of the structure of hemoglobin so, this is, (let me write it here), hemoglobin. This molecule, it’s actually a protein, and this protein is the protein that is responsible for picking up the oxygen.

Now, let’s go into a little more detail. You can see here, that we have these four structures. Those four structures are called, (let’s do that in blue), those are heme groups. All right, so these are the four heme groups. The special thing about these heme groups is that those are the parts where the oxygen is attracted, so, we have O2 that actually comes and binds to the heme groups. As you would imagine since we have four heme groups, we can take a total of four oxygen molecules. So, this is one oxygen molecule here, and we can have another oxygen molecule here, here, and also here. So, this hemoglobin molecule once again, has a capacity to hold four oxygen molecules.

What’s interesting about the hemoglobin is that whenever one oxygen binds to a heme group, that causes the entire hemoglobin structure to undergo a conformational change so, basically changing the site of the molecule whenever one oxygen binds. As you can see here, this is the heme group but, there’s stuff around on it, and you can imagine that it would be relatively hard for the oxygen to get in there and find the right spot.

However, when one binds, it causes a change which opens it up a little bit to make it a little easier for another oxygen to come in and bind. And, when that other oxygen comes in and bind, it causes another conformational change, making it easier for another oxygen to come and bind and, once again, once that oxygen comes and binds here, it makes it easier for another oxygen to come in here and bind to it. So, in other words, as it starts taking up oxygen, it makes it easier for it to take up more oxygen. And then, of course, the opposite will be true. If we have a hemoglobin molecule that has four oxygen attached and, for some reason it gives up one oxygen, that’s going to cause a change that makes it a little harder for the other oxygen to bind. In other words, it becomes easier for oxygen to leave. So, as oxygen leaves, it’s easier for more to leave; as oxygen binds, it makes it easier for more oxygen to bind.

As a result of this, we get a relationship that is shown in this oxygen-dissociation curve. And, what you can see here is, (we’re going to be looking at this blue line) and, as you can see here, it’s not a linear relationship. In other words, as the amount of oxygen increases, so here, we’re showing the pressure of oxygen, as the pressure of oxygen increases in the environment that the hemoglobin is in, you’re going to get more binding, making it easier for more to bind, making it easier for more to bind, and the graph is going to increase faster as you’re going to the right where you have an increased partial pressure of oxygen.

Not a linear relationship but, as some binds it becomes easier so, more bind faster and it becomes easier and it gets faster and faster until, of course, it reaches to where it’s getting saturated and, it dies off.

Now, you might be wondering why it’s not just four-levels since we only have four binding spots for the oxygen, the four heme groups. However, this is not looking at one hemoglobin molecule. This is looking at a bunch of hemoglobin molecules in a bunch of red blood cells and, overall, as some starts binding, it makes it easier and easier so, it’s going to increase faster and faster until it reaches to the saturation and then, it’s going to slow down when it reaches its full saturation.

Also, as you come in this direction, as the pressure of oxygen decreases, and oxygen starts to leave, here it’s leaving slowly but, as it starts to leave more, it’s dropping down faster, and faster, and faster, until all of the oxygen is gone.

So, this is the oxygen-dissociation curve showing once again, as you pick up oxygen, it makes it easier for oxygen to be picked up, so here it starts slow and it goes faster and faster and faster and as you release oxygen, it makes it easier for oxygen to leave and then, that goes down faster and faster. This is called the oxygen-dissociation curve.

That’s pretty much it for this video. If you want to see more videos like this and check out the other resources we have available, visit the website at www.interactive-biology.com.

That’s it for this video and I’ll see you on the next one.

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