060 Hemoglobin and the Oxygen-Dissociation Curve

060 Hemoglobin and the Oxygen-Dissociation Curve

Leslie Samuel IBTV, Physiology, The Respiratory System 141 Comments

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.

Comments 141

    1. Post
  1. Shrikharan

    Dear Leslie

    I think I must correct you. You were not very clear on the interpretation and the proper message offered by the O2 dissociation curve. I am a doctor and O2 dissociation curve is a very important component of respiratory physiology, and understanding of the diseases of the lungs.

    The real purpose of the sigma shaped O2 dissociation curve is to illustrate one important point. For the hemoglobin (Hb) to be saturated fully with O2 at the alveolar end, there must be a PO2 of 75 -100 mm Hg.

    At lower PO2, the Hb will become deoxygenated. To repeat PO2 > 75 mm Hg encourages saturation of Hb where else when PO2 is <75 encourage desaturation of Hb. This is how O2 is transported and delivered to the tissues.

    At the tissue level, where the PO2 is low makes the Hb to become deoxygenated and thus deliver the O2 to the tissue. This is how Hb does its function. It must capture O2 when PO2 is high (at alveolar level) and release the O2 when PO2 is low (at tissue level).

    The real message of the O2 dissociation curve is that at the alveolar level we have to maintain a good PO2 (75- 100mmHg) otherwise, Hb cannot be saturated and thus fails in its O2 transporting ability. O2 is poorly soluble in plasma and thus depends on the Hb to carry it to the tissues.

    Now see the graph again. According to the graph once PO2 drops to below 70 then it reaches a slippery slope and with slight decrease of the PO2 thereafter there is a rapid desaturation of HB (at the alveolar level) and loses its O2 carrying capacity and there is severe O2 lack/starvation by the tissues. PO2 at alveolar level can get affected by breathing O2 lacking air or due to pathology or disease of the lungs and proper gas exchange cannot take place to maintain a good PO2 (>75mmHg) so proper oxygenation of the Hb can take place to produce Oxyhemoglobin.

    This is the real message of the O2 dissociation curve – to see that PO2 does not drop below 75, and if you do, you will go down a slippery slope where a small drop of PO2 will produce a drastic drop in the O2 Saturation.

    1. Post

      Hi there,

      Is that really a correction of what I said in the video? Or does it just look at it from a different perspective? You are right. That would’ve been a good thing to add in the video. However, that’s part of the reason why I have comments enabled. So that people could contribute what they know to what I put here.

      Do you think I said something that was wrong in the video? I’d like to know your answer to that.

      1. Shrikharan

        I think you are not really ‘wrong’ in what you said.

        You missed the main point behind the Sigma shape of the graph. Hb needs the high PO2 to saturate it. Below a point, a small drop in the X-axis produces a remarkable drop in the Y-axis.

        The Sigma has three legs, a horizontal, then a steep oblique and then a horizontal leg.

        This is my understanding. I am a doctor but not really a medical physiologist.

  2. InteractiveBiology

    @eddieyou1018 Oh, you poor guy. Having to listen to my annoying voice, lol.
    It’s really easy though. All you have to do is not watch the videos, and
    everything will be ok. You won’t have to deal with such an annoying voice.
    All the best :D

  3. InteractiveBiology

    @eddieyou1018 Oh, you poor guy. Having to listen to my annoying voice, lol. It’s really easy though. All you have to do is not watch the videos, and everything will be ok. You won’t have to deal with such an annoying voice. All the best :D

  4. InteractiveBiology

    Oh, you poor guy. Having to listen to my annoying voice, lol. It’s really easy though. All you have to do is not watch the videos, and everything will be ok. You won’t have to deal with such an annoying voice. All the best :D

  5. 0326hkim

    !!!! Remember everyone….pH can also be Hydrogen Ion. the arrows would
    just be the opposite. High pH = low H and vice versa !!!!!!! Just in case
    your exam comes out tricky like that.

  6. 0326hkim

    !!!! Remember everyone….pH can also be Hydrogen Ion. the arrows would just be the opposite. High pH = low H and vice versa !!!!!!!

    Just in case your exam comes out tricky like that.

  7. InteractiveBiology

    :) Thank you! Glad you got something out of it. We have more Biology videos in the website, and more to be added so, please stay tuned for more!

  8. othoooo

    wooooooow :) this is greaaaaaaaat vidoe man.. i ve biolgy exam in jan and i’m so glad to find such video >> i’m going to watch the rest :) thank u indeed mate

  9. LilSayWhat

    Actually, it is very difficult for the fourth oxygen molecule to diffuse in and associate with the last available haem group.

  10. newlynappynat

    Bless you for doing this, love your voice and find that you seem to make the most sense for me on YT. great job!

  11. topspinserve94

    Is the haemoglobin inside the red blood cell or is it just floating inside the blood plasma, if its inside the red blood cell doesn’t that lengthen the diffusion pathway making it less effective at picking up oxygen. Great video by the way it really helped.

  12. topspinserve94

    Is the haemoglobin inside the red blood cell or is it just floating inside the blood plasma, if its inside the red blood cell doesn’t that lengthen the diffusion pathway making it less effective at picking up oxygen. Great video by the way it really helped.

  13. Babyxcakes1

    This was the most useful video ever. I have recently started my degree and have never understood this concept so well as I have today! 10 star! Fantastic!!

  14. divisorplot

    Nice audio signature, appreciate the spoken word without the hyper noise noisy music.Information theory ,noise ect. Ture pure puer spoken word lecture.

  15. Nim565

    I’ve been trying to understand this stupid dissociation curve for a year from a lot of different people but somehow i understood your explanation.
    Seriously you’ve helped me a lot!! :)

  16. sarva khitana Bunbulama

    thank you. I was reading about partial pressure of gasses in blood and how that is related to H ions and bicarbonic ions but it was great to watch this now i know what they mean with conformational changes.

  17. mrtigerucantfly

    Does it really matter how haemoglobin is spelt? I’m American and have always spelt certain words the British way….not sure why but to me the British spelling has always seemed correct. Like if my professor writes “liters” on the board, without hesitation I write “litres”, if he writes hemo- I write haemo- and so on….I know weird.

    Well anyway this video has been very helpful. Thank you very much! :-)

  18. gracecamp1

    I know I got confused too, think I worked it out:
    As the conformational change changes the shape of the haemoglobin it makes it easier for O2 to attach. However FIRST the O2 has to DIFFUSE into the red blood cell before it attaches.If you have 3 O2 already in there then it cant diffuse in as the concentration of O2 is too high in the RBC. However if it was near the lungs then the O2 could diffuse in as the concentration of O2 is lower in the RBC than the surrounding enviroment.RBC=RED BLOOD CELL

  19. bunieshit

    I don’t know what’s his problem, but I love your voice :D I love how easily I can understand every word you say, even if english isn’t my first language. If I have something I don’t understand, I come to your channel, because you are my favorite biology teacher online :] I can’t express how much you helped me, I have poor biology skills, but you actually made me understand it. I wish you were my teacher, not like it’s possible or something. :D

  20. MissRosy942

    This is great! im revising for alevel biology and i was struggling with this topic, this has cleared it was up! thanks!
    however did you spell haemoglobin right?? in England we spell it with an “a” before the e!!!

  21. Melissa Norris

    Just like everyone else, I have to say Thank You!! Extremely helpful and your enthusiasm towards this subject makes it much more enjoyable to watch! Blessings!

  22. ThaNosaN

    Thanks a lot for this, after 1 year of studying physiology this is the only tutorial actually opening my eyes on what’s up with the curve! Your voice is so cool it would be insane if you wore dreadlocks as well hehe.
    Keep up with the great work! :)

  23. dorothywx

    Wowzers. This is super-duper-awesomely filled with awesomeness. Yesterday I thought to myself, I dont understand this, why is this so confusing, but after watching this today I can FINALLY say I understand oxygen dissociation curves. woot woot! Yesterday I even thought I could never understand this ever again, now today I am like wow its clear in my head, I can understand it!

    Anyways just want to thank you for your uber awesome efforts


  24. LFCowen95

    You could’ve mentioned the change in the diffusion gradient when the haemoglobin molecule becomes more saturated. It’ll be harder for an oxygen molecule to bind with a haem group when it’s nearly completely saturated because it will be highly concentrated with oxygen so diffusion gradient changes. This explains the decrease in the gradient on the curve towards the end and explains why it’s difficult for 100% saturation. Still a fantastic video though

  25. raquelborn

    THANK YOU. Fantastic voice, nice speed, good use of language, no umming or ahhing. Don’t know what people are complaining about.

  26. ibrahim2ibrahim

    someone please enlighten me because i am very confused… if it becomes easier for other O2 molecules to join the Hb the more there are, how comes the graphs are sigmoid? shouldn’t they become steeper?

  27. cuoredipietra89

    I’m sorry for english I’m an Italian student
    the curve is a sigmoidal curve because it is’ the result of an average between 2 other curves: the curve of high affinity (hyperbolic) that we get when hemoglobin binds O2 in the lungs….and the curve with low affinity (hyperbolic) that we get when hemoglobin leaves the ‘O2 in the tissues. by union of the two curves you obtain the sigmoid as you see in the video. XD

  28. cuoredipietra89

    in effect the video is very simplistic and gives us a vision of elementary’ hemoglobin and its operation that in reality is far more complicated …. luckily XD

  29. gareth davies

    Sorry if I’m wrong, but is it not “haemoglobin”?
    Am i wrong? or does it change for different countries?

  30. Samrina Ahmed

    Heloo Leslie

    I am realy feel excitement to read the comments of ur fans but Leslie in my computer all other videos are properly working except this web site(ww.interactive-biology.com).plz let me know the reason.Is any other softwere used here for working or same other.
    waiting ur reply
    Samrina ahmed

Leave a Reply

Your email address will not be published. Required fields are marked *