2-27 respiratory systems II

2-27 respiratory systems II - RESPIRATORY SYSTEMS, PART II...

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RESPIRATORY SYSTEMS, PART II LIFE 48.4-48.5 48.4 How does blood transport respiratory gases? - blood plasma carries some O 2 in solution , but its ability to transport O 2 is quite limited has molecules that pick up or bind O 2 where its partial pressure is high and release it where its partial pressure is low -hemoglobin increases capacity of blood to transport O 2 by about sixtyfold 48.4.1 Hemoglobin combines reversibly with oxygen - hemoglobin : protein consisting of four polypeptide subunits where each surrounds a heme group —an iron-containing ring structure that can reversibly bind a molecule of O 2 Thus, each molecule of hemoglobin can bind up to four molecules of O 2 - O 2 diffuses into the red blood cells it binds to hemoglobin cannot diffuse back across the red cell plasma membrane hemoglobin maximizes the partial pressure gradient driving the diffusion of O 2 into the cells -ability of hemoglobin to pick up or release O 2 depends on the P O2 of its environment When the P O2 of the blood plasma is high (i.e. in the lung capillaries ) each molecule of hemoglobin can carry its maximum load of four molecules of O 2 As the blood circulates through the rest of the body, it encounters lower P O2 values. At these lower P O2 values, the hemoglobin releases some of the O 2 it is carrying -relation between P O2 and the amount of O 2 bound to hemoglobin is not linear, but S-shaped sigmoidal b/c reflects interactions between the four subunits of the hemoglobin molecule low P O2 values: only one subunit will bind an O 2 molecule shape of that subunit changes causes alteration in the quaternary structure of the whole hemoglobin
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2-27 respiratory systems II - RESPIRATORY SYSTEMS, PART II...

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