The evolution of oxygen carrying proteins represents a major adaptation in the history of life. Overcoming the low solubility of oxygen in water, oxygen carriers make aerobic respiration possible in tissues. The oxygen carriers in vertebrates are myoglobin and hemoglobin. Myoglobin is located in muscle. Hemoglobin serves as the oxygen carrier in blood, increasing its oxygen carrying capacity fifty fold.
The properties of oxygen carriers are worthy of extensive, dedicated focus in MCAT preparation, not only because topics such as the Bohr effect are long-standing favorites. The former was true in the days of the old MCAT and is even more true with the new, biochemistry focused MCAT. Additionally, the properties of hemoglobin are a model for how proteins behave. Hemoglobin provides a model for understanding how a comformational change may alter the pKa of a residue side-chain, for example, and it is the place to learn how cooperativity works in allosteric, multisubunit proteins, both important concepts to bring to enzyme mechanics and regulation.
Conceptual Vocabulary for Oxygen Transporters