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Biology: Human Gas Exchange: Respiratory Pigments


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About this Lesson

  • Type: Video Tutorial
  • Length: 11:41
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 126 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: Animal Systems and Homeostasis (63 lessons, $84.15)
Biology: Gas Exchange and Transport Systems (5 lessons, $9.90)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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You know, just because lungs can suck in oxygen, doesn't mean it's just going to automatically go to every organ in your body. You know you have a transport system, and you know the transport system has a lot of different purposes. But somewhere along the way, I've got to tell you about the role of hemoglobin and blood plasma, and I think I'm going to do that right now. Even though we're not like immersed in this discussion of the transport system, this is literally a crossover system.
Let's talk about hemoglobin. Hemoglobin, as you know, is a protein that is found in your red blood cells, and it consists of four polypeptide chains. Each chain has a heme group, the center of which is iron. And it is the iron, which gives hemoglobin its magic abilities to pick up oxygen as it diffuses across the membranes of the alveolae. So I guess the thing we've got to start out with, number one, is you take in the air, and oxygen diffuses across the alveolae membrane, because there's a concentration gradient. Then you need a molecule that's tough enough to pick up that oxygen, and yet we'll give it up when needed.
That's the key here. You've got to take that oxygen in, put it on a red blood cell, and give it up as needed. And that's where the hemoglobin's going to come in. And you can see that, boy, hemoglobin is a lot more complex structure than this, as you take a look at this beautiful picture of hemoglobin, and you can see the highlighted heme group that stands out there in the middle of each one of those chains, and just looking to pick up oxygen. Well, let's see what happens when hemoglobin indeed does pick up oxygen.
To do this properly, we have to take a look at a graph, and let's make sure this graph can make sense throughout our whole discussion of this thing. Now, let's see, where are we going to put where. The first thing we want to do is we want to make sure that you guys understand what we're seeing here. This here is called a PO[2]. PO[2] stands for partial pressure of oxygen. What that means is concentration in tissues - that's a good way to look at it. So the PO[2] literally is representing the concentration of oxygen in tissues. So, for example, here would be the concentration of oxygen in the lungs. And so in this point right here, that tissue, the lung tissue, is completely concentrated. This would be, say, a tissue at rest, so any kind of tissue when you're not exercising - a non-exercising tissue. And here would be an exercising tissue.
So there's my partial pressures in my tissue. So far so good? In other words, another way to say that is, it represents their need of oxygen. So you're doing aerobic respiration, and, obviously, your lungs don't need a whole lot of oxygen; your non-exercising tissue has a fair amount of need of oxygen, because its concentration of oxygen is low; and exercising tissue, it's way low. Now over on this axis, we're going to be talking about how saturated hemoglobin is - so oxygen saturation of hemoglobin. Well, once again, hemoglobin is very saturated up in here, and look what's happened, and now we get to what's going on.
Let's look at some numbers. Here is what hemoglobin does. Now, do you know anything about an aspect of proteins called cooperativity? You should, and if you don't, you may want to look it up. I'll give you a quickie review of it. What it simply means is this: Some enzymes work in groups, say groups of four, say like a hemoglobin molecule, which isn't an enzyme, but it's going to work nevertheless, and there are inactive and active forms. And when one - and quite often, we picture these as coming in groups of - the one you can look up has groups of four, and what it showed was this, that when this particular, when one of the protein molecules bound with a substrate, it made the other three much more likely to bind with that substrate.
So, in essence, it was a cascading effect - once you bound one to the substrate, the other three bound also. That is the way hemoglobin works. So if you get one of these to bond, you actually get all four to bond. So a saturated hemoglobin molecule in a red blood cell has all four heme groups felt. Now let's take a look at what's going to happen in this graph, and we want to talk about how efficient versus how adaptive. You'll see what I mean in a second. So the lungs take in the oxygen, and everything is fine, and the hemoglobin is 100% saturated. But let's take a look at what happens. If you go down to this point right here, and right now, as I'm - I'm fairly rested, my brain's working like crazy and I've been standing a while, but, you know, my pancreas is just hanging out, and my pancreas is not exercising - not that pancreas's do a lot of exercise - but my arm muscles, they're just kind of at rest right now. So this hemoglobin that's going by my arm muscles is not like really getting ripped off of its oxygen. It's literally coming down here, and it's giving up one of its oxygen molecules - and that's it, because my arm is a tissue at rest. And then it goes by my arm muscle, gives up its oxygen, and scoots back to the lungs where it gets resaturated. And that particular hemoglobin molecule did not give up its oxygen.
Now I'm going to exercise my arms, and now my arms really need hemoglobin - or, excuse me, they really need oxygen. And now they're no longer tissues at rest. So what's going to happen now? You see, now what can happen is they're exercising tissue, and they're going to have a greater affinity for the hemoglobin - for the oxygen. So now what's going to happen is their partial pressure is dropping, their concentration of oxygen is dropping, and my hemoglobin is going to get this oxygen ripped off of it because of the need for my tissues - and it's all to do with partial pressures, which is why we learn about partial pressures in chemistry, so we can learn biology. And so the bottom line is, this is literally an efficient system when you need it. And so it comes down to that: efficiency versus adaptability. If I gave up all my hemoglobins and my resting tissues, what would happen when I exercise? What would happen when I was in oxygen need? I wouldn't have enough. Let me show you a cool extension of this called the Bohr shift. But before I do that, let me tell you that - sometimes, when you do exercise, what do you do? You give off carbon dioxide, right? You know aerobic respiration gives off CO[2]. And you know that CO[2 ]plus water - if you know your biochemistry, you'll remember this - CO[2 ]plus water forms an acid - carbonic acid. So what does that cause to happen? That causes the blood - the plasma - to drop its pH, because it's getting more acidic. So I want to call you a shift called the Bohr shift, which happens in hemoglobin, and it's really quite interesting.
What we have here - we're going to keep the same graph, or the same axis - partial pressure of hemoglobin - and let's take a look at what happens. Now, first of all, let's see the normal. This would be, remember, at about living tissue, normal tissue, we have a 75%, which means we've given up about one out of four of our molecules, right? And that's right here. So this is pre-Bohr shift, so this is pH equals 7.4. But when you get acidic buildup, your pH is going to drop, and the pH of the blood here is 7.2. Look how that is changed - the oxygen-giving capabilities of hemoglobin. In other words, what's going to happen now, at this particular one, the hemoglobin is - well, let's see, let's looking at the living tissues. What has happened here?
The hemoglobin at this point is less saturated, isn't it? It's down to 60, whereas here it was at 75. Why is that? Well, think of the message you're sending. When you have a buildup of CO[2 ]and you have a buildup of acid, what does mean? It means you're exercising a lot, and if you're exercising a lot, what does mean? You need oxygen. And when you need oxygen, what does that mean? You're going to rip it off hemoglobin. So this Bohr shift is literally your way of getting more hemoglobin - sorry, more oxygen - off of your hemoglobin, and it's part of the biochemical nature of hemoglobin. That's very cool stuff.
Let me tell you about one more thing. Let me tell you about myoglobin. Myoglobin is another protein a little bit like hemoglobin, but it holds the oxygen still harder. So if I were going to add myoglobin to this scale, I'm not going to be perfect on the axis, but let me show you the general tendency. It's a single-chain polypeptide, it holds oxygen harder than hemoglobin, and it's used and stored in muscles, it's particularly used in muscles; so it's a special form of globin found in muscles - and look at this graph. This is much higher. Why? It holds its oxygen more. Why? Well, think about this: At exercise - which muscles do all the time - it's going to - see, it's going to give up its oxygen less readily until you need it, and then, because it's there in the muscles, it's there to give up its oxygen. And so myoglobin is a specialized pigment that's going to give up its oxygen to things when they really need it. And it differs from organism to organism. For example, if I were to add fetal hemoglobin to this chart, fetal hemoglobin holds its oxygen a little big more than maternal hemoglobin. And here's the best one, I love this one - think of creatures that live high in the air where there's very little oxygen. So that creature - high in the air, high in the mountains, where there's very little oxygen - that creature is going to have a hemoglobin that's going to hold its oxygen harder, because its tissues are going to be different. And a lot of hemoglobin is right up here.
So a lot of hemoglobin is going to get rid of its oxygen at still different partial pressures than the other ones. Very cool stuff - seals, whales, man, they are loaded with myoglobin, and that's why they can dive way deep. They have their spleen, their spleen holds 5 liters of blood, so they're loaded with hemoglobin, they're loaded with myoglobin - they can hold their breath for an awfully long time.
So I just want you to know that it's the oxygen carrying that is so important, but let's not forget carbon dioxide. How do we get carbon dioxide out of our body? I'll tell you that one next.
Animal Systems and Homeostasis
The Human Gas Exchange and Transport Systems
Human Gas Exchange: The Roles of Respiratory Pigments Page [2 of 2]

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