So what hemoglobin does is it essentially continually delivers the oxygen from the lungs and to the tissues and cells of our body. And it also binds CO2 and brings the carbon dioxide back to the lungs so that the carbon dioxide can be expelled by our body. Now, in this lecture, what I'd like to focus on is how these two proteins actually are capable of binding to oxygen in the first place. So these two proteins contain a special prosthetic group known as the hein group that assists the protein in actually binding the oxygen. And the heme group has the following structure. So the heme group consists of two components.