rder to understand the transportation of oxygen and carbon dioxide at a molecular level, it is important to understand the structure of Hemoglobin (Figure). A heme group consists of an iron (Fe) ion (charged atom) held in a heterocyclic ring, known as a porphyrin. As seen from the figure the iron ion is the site of oxygen binding, bonds with the four nitrogens in the centre of the ring. The iron is also bound strongly to the globular protein. A sixth position can reversibly bind oxygen, completing the octahedral group of six ligands. Oxygen binds in an "end-on bent" geometry where one oxygen atom binds Fe and the other protrudes at an angle. When oxygen is not bound, a very weakly bonded water molecule fills the site, forming a distorted octahedron.
Oxyhemoglobin is formed during respiration when oxygen binds to the heme component of the protein hemoglobin in red blood cells and occurs in the pulmonary capillaries near the alveoli of the lungs. The oxygen then travels through the blood stream to all the tissues and cells where it is utilized in aerobic glycolysis and in the production of ATP by the process of oxidative phosphorylation. Deoxyhemoglobin is the form of hemoglobin without the bound oxygen (Wikipedia, 2007).
Bicarbonate ions react with the Hydrogen ions that are released from reduced hemoglobin and are in turn converted to water and carbon dioxide. For this reaction to occur an enzyme called Carbonic Anhydrase is required as a catalyst. The end product of the reaction is water and carbon dioxide which are then exhaled.
HCO3- + H+ -----> H2CO3 -----> CO2 (exhaled) + H2O (exhaled)
To put it in simple terms hemoglobin can bind oxygen and carbon dioxide. The amount of oxygen bound to