Now, one important property of hemoglobin, one important property that hemoglobin actually exhibits is something known as positive cooperativity. Now, what exactly is positive cooperativity? Well, when one oxygen molecule is taken up by the hemoglobin, it causes a conformational change. It causes a change in the three dimensional structure of the entire hemoglobin. And as the structure changes, it makes it much more likely to actually pick up other oxygen molecules. So as soon as our deoxy hemoglobin picks up a single oxygen, it changes its shape ever so slightly, and it changes the shape in such a way that it makes it much more likely to pick up other oxygen molecules.