hemoglobin
"Hemoglobin is like the pimp that brings the four girls to the club"
"Ok, so there's alot of information covered above! We've been buzzing around this subject since back in BIO-100 when we talked about carrier proteins and Mrs. Gess did the football player tucking the ball into a safe hold in order to get it up the field. In this case, the football player is hemoglobin and oxygen is the ball. The only difference is that hemoglobin is like a multi-handed player because it can actually carry up to four oxygen's at a time!"
"Thus hemoglobin is like an efficient sponge that soaks up oxygen so more can enter the blood. Hemoglobin continues to soak up oxygen molecules until it becomes saturated with the maximum amount it can hold - an amount that is largely determined by the PaO2. Of course this whole process is near instantaneous and dynamic; at any given moment a given O2 molecule could be bound or dissolved."
"Oxygen dissolved in the plasma will first enter the red blood cell. As the dissolved oxygen concentration inside the cell increases, hemoglobin will begin to bind the oxygen. Each hemoglobin molecule is a tetramer consisting of four subunits, and each subunit binds one oxygen molecule. Therefore, each hemoglobin molecule can bind a total of four oxygen molecules. Once the oxygen is bound to hemoglobin, it no longer contributes to Po2. Thus, hemoglobin is like a "sink" that can take up oxygen until each hemoglobin molecule is fully (100%) saturated with four oxygen molecules. "
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