We have alpha one, alpha two shown in green, and we have beta one and beta two shown in orange. Now, when we form the adult hemoglobin, the adult hemoglobin actually contains a cavity inside a space that is capable of binding a molecule called two three BPG. Now, what exactly is two three BPG? Well, two three BPG is a molecule that is a byproduct of cellular respiration. So when cell respiration takes place inside the cells of the adult individual, they produce two three BPG. And two three BPG can actually bind into that cavity into the space that is found in the adult hemoglobin.