hello and welcome to learn a level biology for free with mr. stroke this video is going to be on the transport of oxygen by hemoglobin there will be a few questions as we go or you might want some pen and paper to make notes as well so first it's just a bit of a recap and that is thinking back to what is the function of a red blood cell and can you describe the structure of a of the protein hemoglobin so they'll be linking back to one of the earlier topics in year 12 so pause the video and just have a think about that so the first one the function of the red blood cell so red blood cells contain hemoglobin and that is so they can transport oxygen in the blood and the structure of hemoglobin is a quaternary structure at prating meaning it contains more than one polypeptide chain but each of those polypeptide chains is still folded into the 3d unique shape and hemoglobin has four polypeptide chains and each of these change chains contains a hue the heme groups have iron within them and this is where the oxygen would bind so a little bit more about them as well there's not just one hemoglobin protein it's actually a group of proteins which he find within different organisms and different tissues of the same organism and that different types of Engraving affects its ability to attract load and unload oxygen so for example another type of hemoglobin here myoglobin which is able to store and hold on to oxygen even at very very low partial pressures of oxygen so some key phrases just to be familiar with as we start to go through the oxyhemoglobin dissociation curves these four here so affinity of saturation loading association or unloading and dissociation so affinity is the ability of hemoglobin to attract or to bind oxygen to it saturation is when the hemoglobin is holes in the max amount of oxygens it can bind loading or Association is when oxygen is binding to hemoglobin and unloading and dissociation is the opposite so that is when oxygen is detaching or unbinding from the hemoglobin so these are phrases that will be used as I said when you're describing the oxyhemoglobin dissociation caps so here it is the oxyhemoglobin dissociation curve this curve is described as a sigmoid curve so it's a slight s-shaped curve what this is demonstrating to us is that when oxygen is loaded at a high partial pressure so this part of the graph we can see that is at almost 100% saturation so at high partial pressures which means a high concentration of oxygen hemoglobin will be almost completely saturated with oxygen at low partial pressures or lower partial pressures we only have about 50% saturation so we have a lower partial pressure of oxygen hemoglobin doesn't have as high in affinity so it won't attract the oxygen as well and as a result it will actually unload oxygen in those regions and this is an advantage because if we think about areas within an organism which would have a low partial pressure of oxygen that would be anywhere within the organism that is respiring because they'd be using up the oxygen in respiration and therefore there'd be a low partial pressure so the reason then it's an advantage that our low partial pressures there is a lower affinity it means that you're unloading the hemoglobin is unloading the oxygen at sites where the oxygen is needed conversely at the higher partial pressures we have almost 100% saturation of oxygen which shows that hemoglobin behaves in a manner in which a high partial pressure it has a high affinity for oxygen so it will be loading or associating lots of oxygen so that means where there is lots of available it will load it up so then when it is transported in the red blood cells in the blood it can be unloaded at areas where respiration is occurring so that's our oxy hemoglobin dissociation curve and here is our explanation of that curve a bit more there about why hemoglobin has these different properties at different partial pressures and this is to do with cooperative binding so this is the idea that at this low partial pressure we don't have a very high saturation and this is explained by this bit here so the first oxygens to bind to hemoglobin is actually very difficult for them to bind but once they do bind it makes it much much easier for the other oxygens to bind and that's because hemoglobin is operating so once the first oxygens bind slightly changes that 3d shape so it's then easier for the subsequent oxygens to bind and that's why we have this steep steep curve because once the first is bound is there much much easier for the final ones to bind until we reach saturation so the next idea then is how different conditions affect hemoglobins affinity and one example you need to know is the Bohr effect and this is a description of the effect of carbon dioxide so the Bohr effect is when there's lots and lots of carbon dioxide present and carbon dioxide will form carbonic acid when it is dissolved in the water within blood so if there's lots and lots of respiration occurring lots of carbon dioxide dissolves in the blood blood becomes acidic and the effect this actually has is the oxyhemoglobin curve shifts to the right and if the curve has shifted to the right what actually means is he MacLean is affinity for oxygen has decreased and if the affinity is lower then it will more readily unload oxygen so if we just have a look at some comparisons of these curves we've got here seven point six so that point it's not it's the least acidic out of these three lines so that must mean there's a low partial pressure of carbon dioxide because we have the least acidic conditions and that's likely to be in the alveoli because that's where the carbon dioxide will be diffusing out so at that point in the blood you won't have a high partial pressure at all carbon dioxide so the oxyhemoglobin curve shifts to the left and therefore the hemoglobin has a higher affinity if it shifts to the left I'll upload more oxygen if we have a look then at our most acidic curve is still not particularly sitting at 7.2 in this example but the curve is shifted to the right and that's because we have a high partial pressure of carbon dioxide at this particular point so that could be in respiring tissues where carbon dioxide's being produced it then dissolves into the blood and you have more acidic blood and that then cause is the shape of the hemoglobin to change slightly and that slight change in shape of the hemoglobin causes the affinity to decrease and therefore it unloads the oxygen more readily so that's why this particular point we've got the same partial pressure so just over 20 however exactly the same partial pressure for the seven point six ph curve the saturation is just over 60% whereas the curve 47.2 it's about twenty-five to thirty percent so it's shown us that even at the same partial pressure of oxygen if you have more carbon dioxide present the affinity decreases and the way we can see that is there's a low saturation so more oxygen must have been unloaded because there's a lower affinity whereas if you don't have calm dioxide or as much carbon dioxide present you have a higher affinity shown by the higher saturation of oxygen it must be attracting and Load more readily and that's an advantage because again means that respiring tissues oxygens being unloaded so Arabic respiration can continue so you get maximum quantity of ATP being produced so muscle contraction can continue so the final idea is the fact that different animals have different types of hemoglobin and each of those types of hemoglobin have different affinities for oxygen and that is so that they can adapt their particular environments so if we have a look at the fetal hemoglobin first of all and on this oxyhemoglobin curve were just gonna focus on the adult hemoglobin which is shown as HB a and the fetal hemoglobin which is hbf and the key thing is always to look at has the curve shifted to the left or the right in comparison and for this one the fetal hemoglobin has shifted the curve is shifted to the left of adults and if it's shifted to the left what that tells you is that even at the same partial pressure of oxygen so if we look at 25 if the curve shifted to the left that means it must have a higher affinity so the same partial pressure is more saturated in oxygen so we've got probably around 70% saturation whereas for the adults it's under 50% saturated so the fetal hemoglobin is slightly difference that adult hemoglobin and that has a higher affinity for oxygen even at the same partial pressure of oxygen and the reason that's an advantage is the fetus can't inhale and exhale is only source of oxygen is from the mothers hemoglobin in the blood supply coming through the placenta so the fetal hemoglobin must have a higher affinity for oxygen in order for it to be able to grab the oxygen from the adult hemoglobin and that's how a fetus is able to get and pick up and load oxygen from its mother's blood and from its mother's hemoglobin next example we have is a llama llamas are found at higher altitudes where there is a lower partial pressure of oxygen so that's why it's an advantage again if you've have a look the curve has shifted to the left which means that the llama hemoglobin has a higher affinity for oxygen compared to human hemoglobin so we even have the same partial pressure we have a look at 40 you can see the human hemoglobin maybe about some types unsaturated whereas the llama hemoglobin about 80% saturated so even at the lower partial pressures of oxygen which is what the llamas environment would have it will still be able to load the oxygen a dove so this time the Dove the curve has shifted to the right and if you see the curve shift to the right that means that the hemoglobin has a decreased affinity for oxygen so be more likely to be unloading the oxygen at the same partial pressure and the reason this is an advantage is doves have much faster metabolisms than humans and that's because they have lots of muscle contraction particularly when they're flying so in order to be able to meet that respiratory need for muscle contraction they need a much much higher supply of oxygen to continue aerobic respiration so their hemoglobin has a lower affinity so be more readily unloading the oxygen so that the respiring tissue has a constant supply for aerobic respiration last one is the earthworm so earthworms mainly live underground where there'll be a lower partial pressure of oxygen so again they require hemoglobin with a higher affinity so even if underground where there's very very low partial pressures of oxygen they'll still be able to attract and load up with the oxygen that they require so in summary we went through the beginning hemoglobins are proteins which you have in different animals and there's different types it's a quarter nary structure and the hemoglobin in red blood cells are responsible for transporting the oxygen the oxygen is loaded in regions of high partial pressure of oxygen say for example the alveoli in humans and it's unloaded in regions of lower partial pressures such as requirement issues and that's demonstrated on the oxyhemoglobin dissociation curve by that sigmoid shape curve the co-operative nature of oxygen binding team globin is due to that idea who said where hemoglobin actually slightly changes shape when the first oxygens bind and that slight change in shape makes it easier for the further oxygens to bind the Bohr effect is when there is a high carbon dioxide concentration and that causes the curve to shift to the right and that shift to the right always indicates that the affinity for oxygen has decreased and in this circumstance the Bohr effect the reason for that decrease in affinity is because calm dark site will make the blood slightly more acidic and that changes the shape of the hemoglobin slightly this is an advantage it because that means it's going to more readily unload oxygen activist parent tissues so our last point was looking at the father animals are different types of hemoglobin and there's different types of hemoglobin have different affinities for oxygen and this is an adaptation to their environments so that they can either load oxygen readily even though there's a low partial pressure or it could be due to their movement and muscle contractions they have a high metabolic rate so therefore they need to unload oxygen more readily so that they can meet their respiratory needs so that's it for transport of oxygen by hemoglobin you can find more questions or questions on this topic at missus truck.com where you can practice and test your knowledge if you haven't subscribed already just make sure you click the button to subscribe to make sure you keep up to date with all the latest videos too you with your revision