in this video we're going to talk about Hemoglobin is positive cooperative ity. And so, of course, we already know from our last lesson video that hemoglobin displays positive cooperative ity. And really, it's this positive cooperative ity that allows hemoglobin oxygen binding to display sigmoid all behavior, which, of course, just means that it's going to have an s shaped curve on a saturation curve. And so if we take a look down below at our image notice what we have is a saturation curb where we have the fractional saturation fada on the Y axis and then on the X axis. What we have is the concentration of ligand or the concentration of oxygen gas. And so notice that hemoglobin curve is here in red and hemoglobin is actually displaying sigmoid all behavior because it has this s shaped curve and this is all due to hemoglobin is positive cooperative ity. And so recall from our previous lesson videos that positive cooperative iti is just when the binding of one like end molecule actually makes it easier for other ligand molecules to bind to the proteins. And so, in other words, what we can say is that positive cooperative ITI is when the binding of a lie gone to a sub unit actually promotes neighboring sub units to take on the our state, which is the relaxed state and binds Liggins Mawr efficiently, allowing the Liggins to bind easier to the protein. And so one thing that's important to note is that cooperative ITI in general actually requires multiple sub units. And so, because myoglobin on Lee has one single sub unit, it does not have multiple sub units, and that means that it does not display cooperative ity. And so myoglobin zones. Oxygen binding curve is not going to be sigmoid all, and instead it's actually going toe display a rectangular hyperbole. And so if we take a look down below at myoglobin oxygen binding curve, which is this black curve here, notice that it is not sigmoid all, and instead it displays a rectangular hyperba. And this is all due to the fact that myoglobin has no cooperative ity and so in our next video will be able to talk about the exact models that explain. Hemoglobin is positive. Cooperative it. So I'll see you guys in that video

so recall that way. Back in our previous lesson videos, we had talked about two different models that can explain an Alice Derek proteins, positive cooperative ity and sigmoid all curvature and those two different models where the concerted model as well as thes sequential model. And so it turns out that hemoglobin oxygen binding behavior is actually best explained via a combination of both the concerted as well as the sequential models. And we'll be able to talk more about this idea of how this is a combination of both of these models for hemoglobin. Later in our course, when we talk about hemoglobin is hill plot. But for now, what I want you guys to know is that moving forward, we're going to represent de oxygenated. Hemoglobin is just H B and D. Oxygenated hemoglobin is going to be in the inactive tense T state, which binds like and or oxygen very inefficiently. And then we're also going to represent oxygenated hemoglobin as just HBO to even though we know that technically, its chemical formula would be H H B 024 when it's bound toe all four oxygen's, we're just going to represent it in this way in a more simplified fashion, Uh, just for, uh, easy on the eyes. And so the oxygenated hemoglobin is going to be in the actively relaxed our state, which binds toe like and much, much more efficiently. And so over here on the left hand side, what we have is a reminder of the concerted model as well as the sequential model as it applies to hemoglobin. And so recall that with a concerted model, the hemoglobin protein is going to transition from its T state to it's our state simultaneously in a concerted fashion, where all of the sub the units of hemoglobin are going to simultaneously convert from the T state to the our state and vice versa. Whereas recall that with the sequential model hemoglobin is conversion from its T state to its, our state is going to occur sequentially in each individual sub unit. And, uh, the positive cooperative ITI is going to be displayed through these altered neighboring sub units who get increased oxygen binding affinity. And so we can say here that, uh, hemoglobin positive cooperative ITI is directly being shown here with this altered confirmation with increased oxygen binding affinity and so over here On the right hand side, what we have is a saturation car very similar to the ones that we had seen in our previous lesson videos, where we have the fractional saturation which is either theater or why on the Y axis and then on the X Act is what we have is the concentration of ligand or the concentration of oxygen gas. And so notice that we have these three different curves here in our, uh, plot. And so notice that we have this black curve here which is a rectangular hyperba which we know represents no cooperative ity. And then what we have are these two curves the blue curve as well as the red curve which are actually very, very similar to each other, however, noticed that they're labeled differently. And so this blue curve here actually represents hemoglobin. If Onley, the concerted model applied to hemoglobin and this red curve that we see here represents hemoglobin, actual binding curve. And so what you'll notice is that hemoglobin actual binding curve does not perfectly overlap with the concerted model Onley curve. And so what this means is that hemoglobin does not Onley display the concerted model. It actually does display some features of this sequential model. And, of course, because hemoglobin is curve is so close to the concerted model that is also suggesting that it must display some features of the concerted model is well. And so. This plot here is somewhat of evidence to show that hemoglobin oxygen binding behavior is explained through a combination of the concerted and sequential models. And so we'll be able to get some practice utilizing these ideas as we move forward in our course, so I'll see you guys in our next video.

in this video, we're going to talk about oxygen binding curves, which are actually very similar to the previous saturation curves from our previous lesson videos. And so really, the main difference between oxygen binding curves and the previous saturation curves from our previous lesson videos is the X axis. And so oxygen binding curves will plot the fractional saturation, which is abbreviated as data or capital. Why on the why access, just like our previous saturation curves, did so really no change here on the Y axis, however, oxygen binding curves. Instead of plotting the concentration of the like an and units of morality on the X axis, it will actually plot the partial pressure of oxygen on the X axis. And the partial pressure of oxygen is abbreviated as just p And so we can see that down below. That oxygen's partial pressure, or p 02 is being plotted on the X axis. And so the reason that the partial pressure of oxygen is being plotted on the X axis here is because oxygen 02 is actually a gas and gas is and science are typically measured using their partial pressures. And so the partial pressure of oxygen or the Po two is a completely standard way to be able to express the concentration of oxygen, which again, when it's in this format like this, usually the units are going to be in molar ity. However, when it comes to the partial pressure of gas is the unit is going to be a unit of pressure and, ah, unit of pressure. An example of a unit of pressure is the tour. And so what's important for you guys to know is that the partial pressure of oxygen is actually directly proportional to the concentration of oxygen gas. And so what this means is that the partial pressure of oxygen? We can really think of it in the same way that we think about the concentration of oxygen. And so really, all we're saying here is that moving forward, we're going to be using the partial pressure of oxygen on the X axis. And so taking a look at this curve that we have here this red curve notice that we're showing hemoglobin oxygen binding, which is showing sigmoid all behavior due to its positive cooperative ity. And so what? I want you guys to note here is that the partial pressure of oxygen is actually going to dictate, uh, hemoglobin, oxygen, affinity, and so at very, very low. Partial pressure is very far to the left. Hemoglobin is mainly going to be in its ti state, and the T state we know is the 10th state and has a very, very low affinity for oxygen. And so this region that it's being pointed to down here is referring to hemoglobin when it has a very, very low affinity for oxygen. And then, of course, as we increase the partial pressure of oxygen from left to right on the X axis, oxygen will begin toe bind to hemoglobin, and hemoglobin is cooperative. ITI is coming into play. And so what I want you guys to note is that ultimately, uh, hemoglobin is going to reach a very, very high affinity state, and that is when all of its sub units are going to be in the our state. And so essentially, what we're seeing is that increasing the partial pressure of oxygen is actually increasing hemoglobin affinity for oxygen. And so what this means is that oxygen itself is acting as a homo tropic ballast Eric Activator, which recall from our previous lesson videos. Homo homo just means the same. And so Homo Tropic is just referring to the fact that oxygen binding actually increases. Hemoglobin is ability to bind mawr oxygen. And so because oxygen is increasing the binding of itself, it is going to be a home. A tropic, uh, Alice Terek affect er And so the reason that it's activating is because it's actually increasing Huma global oxygen affinity. And so, really, this is what induces the positive cooperative ITI in hemoglobin. Subunits is the fact that oxygen acts as this Alice Terek activator and so down below right here. We're just emphasizing this same exact idea right here by saying that oxygen is a homo tropic, a lost eric activator that essentially is going to promote additional binding of oxygen to hemoglobin. And again, this is just reinforcing. What we already knew about hemoglobin is positive cooperative ity. And so this year concludes our introduction to oxygen binding curves, and I'll see you guys in our next video

in this video, we're going to talk about how hemoglobin is positive. Cooperative ity actually makes hemoglobin a much better oxygen transporter than myoglobin. And so recall from our previous lesson videos, we said that positive cooperative ity as it relates to hemoglobin just means that binding of oxygen to hemoglobin is going to stimulate hemoglobin to bind even mawr oxygen. And so, really, it's this positive cooperative ity that allows hemoglobin to be a much better deliverer and transporter of oxygen to the tissues than its counterpart myoglobin, specifically for two reasons. Reason Number one is that myoglobin cannot transport oxygen to the tissues simply because it has such a low K d. And of course, we know from our previous lesson videos that ah lo que de corresponds with a high oxygen affinity and a high oxygen affinity, of course, means that myoglobin is going to have no problems binding to oxygen. However, myoglobin binds so well toe oxygen, even at low partial pressure of oxygen that it simply does not want to release oxygen when it gets to the tissues. And so myoglobin simply cannot be a transport of oxygen to the tissues because it would not release oxygen once it gets to the tissues. Now, the second reason that hemoglobin is a much better deliver and transporter of oxygen to the tissues than myoglobin is because hemoglobin is an al assed eric protein that displays the threshold effect. And this threshold effect in hemoglobin allows hemoglobin to optimize its oxygen, released to the tissues. And so hemoglobin is able to release mawr oxygen to tissues that air working harder and depleting more oxygen so they have lower oxygen. And so again, this means that hemoglobin can release more oxygen to the tissues that, um, have a need mawr oxygen. And so, if we take a look at our oxygen binding curve down below notice on the Y axis, what we have is the fractional, saturation theta, or why, and then on the X axis. What we have is the partial pressure of oxygen and notice that we have these two different curves. We've got this black rectangular hyperbole curve for myoglobin, and then we've got this red sigmoid curve here for hemoglobin. And, of course, we have these light colored backgrounds to represent the partial pressure of oxygen in the lungs. Over here, in light blue which is right around about 100 tours. And then we've got this light green background for the partial pressure of oxygen in the tissues, which is ranging somewhere between 20 tours at its lowest to about tours at its highest. And so what I want you guys to notice is that for this black curve here for myoglobin, it's K D, which corresponds with a fractional saturation of 0.5 is showing up at a very, very low value of about 2.8. And that's very, very low with respect to the KD of hemoglobin, which is at 26. And so essentially a lo que de we know means a high oxygen affinity. And so he myoglobin is oxygen. Affinity is so high that it does not want to release oxygen once it gets to the tissues, and so we can see here that in the lungs, both hemoglobin and myoglobin curve are very, very high and binding. The theta is really, really close to about one. However, once we get to the tissues, we can see that myoglobin and hemoglobin is curves are separating from each other, and so notice that my global's curve even at the lowest partial pressures of oxygen and the tissues is not really changing much from when it was in the lungs. And so it's not really releasing that much oxygen at all when it's in the tissues, making myoglobin a horrible oxygen transport. However, hemoglobin, on the other hand, is showing this threshold effect here, where it's able to essentially optimize its oxygen release to the tissues, and so notice that tissues that have a higher partial pressure of oxygen they do not need as much oxygen as tissues that have low oxygen. And so, uh, notice that hemoglobin will release a smaller amount of oxygen to tissues that have higher partial pressure of oxygen. And then hemoglobin will release a much greater partial pressure. Uh, hemoglobin will release a lot more oxygen to tissues that have a much lower partial pressure of oxygen. And so this is what allows hemoglobin to be the best in an excellent transporter and deliver of oxygen. And so notice over here on the right. What we're showing you is a little circulatory system here, and of course, it's showing how blood is delivered and transported throughout our bodies. And so here in the center. Of course, what we have is our hearts which act as a pump to pump the blood throughout our bodies. Now, at the top here, what we have is the blood as it relates to the lungs. And so here what? We have some information and notice that this information corresponds with what we're seeing over here in our plot. So the partial pressure of oxygen in the lungs is right around 100 tours. We can see that here in our plot and notice that hemoglobin saturation in the lungs it's right around 98%. So it's really, really high here and notice that my global saturation in the lungs is really similar. It's also nine. It's about 99% which is really close to 98%. So really, they're binding in the lungs is pretty much the same, however, noticed that, um, the binding is much different between hemoglobin and myoglobin when it comes to the tissues down below. So again, the partial pressure of oxygen in the tissues we can see at its lowest end is right around 20 tours and notice that hemoglobin saturation in the tissues is on Lee, 32% which means that if we subtract, if we do, 98% minus 32% will get 66%. And 66% is how much oxygen is released. So so two released by hemoglobin. And so that is a good percentage of oxygen. And if we do the same for myoglobin saturation in the tissues, notice that its own it's, uh, it's at 95%. And so if we do 99% minus 95% that's Onley 4% oxygen release and so 4% is really, really low. That's not enough oxygen to be delivered to the tissues. And that's why again, myoglobin is such a poor deliverer of oxygen to the tissues. And so the last point here that I want to leave you guys off with is that these, um, this hemoglobin curve because it is an al hysteric protein, it can actually be affected by other Alice Terek defectors Hetero Tropical Hysteric Effect er's such as B p G, for instance, which will talk more about later in our course, and B P G can further enhance hemoglobin release of oxygen to the tissues, making hemoglobin and even better oxygen transporter and deliver to the tissues. And so here what We've emphasizes that hemoglobin is positive. Cooperative ity makes it a better transporter oxygen transporter than myoglobin. And so a zoo we move forward in our course will be able to apply a lot of these concepts that we've learned. So I'll see you guys in our next video.