Oxygen Hemoglobin Dissociation Curve is the topic du jour, and I am going to do my best for you to not get bored. Well, welcome to another MedCram lecture. We're going to talk about the effect of different things on the oxygen hemoglobin dissociation curve.
So we've got a red blood cell that kind of looks like that with a little bit of a bulge in the middle, and that's because it's lost its nucleus. What this is you have to remember is simply a bag of hemoglobin it's got no nucleus it's got no mitochondria so the only form of energy that it can do is glycolysis and remember that's where we get glucose and it goes to basically go to pyruvate and that gives off forms of ATP this is not oxidative phosphorylation this is substrate level phosphorylation but it gives the cell the ATP that it needs and that's important because there's an intermediate in this glycolysis that's actually going to do something story hemoglobin binding curve which we're going to talk about next but before we get to that I wanted to explain to you what the hemoglobin molecule looks like if you can kind of imagine it's four different subunits that are connected to each other okay and usually there's two alphas and two betas but that's not important right now so there's for binding spots for oxygen to bind to so if it binds to the first spot what happens is it causes a conformational shift with the next one that causes oxygen to bind more affinity and that causes a conformational shift with the next one which causes the oxygen to bind even more affinity and finally that causes a conformational shift that causes the last one to bind with even more affinity and so what happens is you get something called cooperativity.
The other term that they like to use in biochemistry is called allosteric interaction in this case it's not allosteric inhibition because it's actually making these globin molecules more apt to bind the oxygen molecule the other thing that you might want to be aware of is sometimes they have different terms for these hemoglobin sub units if they are not bound to oxygen they're known as the tense form or T and if they get bound to oxygen then they're known as R or the relaxed form the other thing that happens that you may want to know is that when an oxygen binds to this hemoglobin molecule a little carbon dioxide molecule comes off a little co2 and you should probably know that that's known as the Haldane effect just some trivia there so that when oxygen binds to hemoglobin it releases co2 and if you see the co2 go up a little bit that's known as the Haldane effect but let's talk about the human lobe and binding curve so the way that this is represented we've kind of talked about this before in the other lecture on delivery of oxygen is there's a relationship between the partial pressure of oxygen in the blood and the saturation of the humic loeben molecule so this is saturation here and this is PA o2 and we can take that all the way up to a hundred so this is a hundred this would be 50 this would be 25 to 75. This is the po2 what we're talking about here and up to about eighty. We're starting to see here that there's a kind of a curviness to this hemoglobin binding curve.
The key points here that I want to show you is that there's this sort of a plateau area here where increasing levels of po2 will not yield much more in terms of the saturation so there's kind of a diminishing marginal utility in sociated with that the other thing I want you to sort of notice is that if we were to shift this human blown hemoglobin binding curve to the right in other words if it were to go from this point to this point notice that in fact what you're seeing here is you're seeing the hemoglobin molecule as a whole being more apt to release oxygen it's more apt to release oxygen and why is that because at any given po2 let's say 50 in this case you'll see that in the blue hemoglobin binding curve has a lower saturation then the yellow hemoglobin binding curve and so therefore the blue hemoglobin binding curve is more apt to be less saturated at a given po2 than the yellow hemoglobin binding curve and that's important because what's actually happening as this thing is shifting back and forth as it goes through the bloodstream depending on where it is so this is kind of something that you should know so here's a question what are some things that are going to shift the hemoglobin binding curve to the right and remember these are things that make it less affinity so the things that make the hemoglobin binding curve less affinity to oxygen or all of the things that you would expect to find in the blood where oxygen needs to be given off by the hemoglobin molecule and that would be in the muscles or placenta and what are they what do you find in the muscles are you going to see a high or a low pH you're going to see a low pH because this is where lactic acid is being produced this is where carbon dioxide is being given off and we know that carbon dioxide is a Lewis acid number two we would see a high temperature okay your muscles are hot right when they're working so that would shift it to the right we already said that a high partial pressure of carbon dioxide is going to shift the hemoglobin binding curve to the right another thing that shifts it to the right is a molecule called D e P G die phosphoglycerate otherwise known as to 3b PG or bisphosphoglycerate this as you may recall is an intermediate of glycolysis and this is where 3-phosphoglycerate goes to to phosphoglycerate and that's an important step in glycolysis because as that happens and as you have this buildup of 2 3 BPG which is by the way seen elevated in pregnancy which makes sense because in pregnancy you're going to want your hemoglobin molecule to be able to give up more oxygen to the fetus you're going to do that you're going to see this increased in pregnancy and you're going to see your hemoglobin molecule giving up more oxygen to the fetus and you're going to see this hemoglobin molecule shift to the right okay now what are some things that you would see cause it to shift to the left these are things that you would see in the lungs so for instance in the lungs you're breathing off carbon dioxide you could have a low acidity so you're going to have a high pH of course in the lungs you're breathing in air which is cooler than body temperature so generally speaking you're going to have a low temperature number 3 as we already mentioned we're going to have a low partial pressure of carbon dioxide and of course 4 we're not going to see maybe possibly as much DPG and so you're going to see a shift to the left the other thing that'll shift it to the left is fetal hemoglobin so H not a but actually F which is way out here ok and that's fetal hemoglobin sucks up that oxygen like no other human globin as it comes by the placenta so that is the hemoglobin molecule and the disassociation curve thanks for joining us you you.
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