Final Answer:
Mb has a hyperbolic shape when graphed %sat vs. pO₂ because of its high oxygen affinity. Thus, the correct option is A.
Step-by-step explanation:
Firstly, the term "Mb" refers to myoglobin, a protein found in muscle cells that plays a crucial role in oxygen storage and release. When graphed, the relationship between the percent saturation of myoglobin (%sat) and the partial pressure of oxygen (pO₂) typically forms a hyperbolic curve. This hyperbolic shape is indicative of a protein with high oxygen affinity, as myoglobin has a strong binding affinity for oxygen, allowing it to readily bind and release oxygen in response to changes in oxygen tension.
Secondly, the hyperbolic curve observed in the %sat vs. pO₂ graph for myoglobin reflects its cooperative binding behavior. Myoglobin exhibits positive cooperativity, meaning that as oxygen binds to one subunit of the protein, it enhances the affinity of the remaining subunits for oxygen. This cooperative binding behavior contributes to the efficient loading and unloading of oxygen in tissues with varying oxygen levels. The hyperbolic shape is characteristic of proteins with cooperative binding, in contrast to the sigmoidal shape seen in proteins with negative or no cooperativity.
In conclusion, the hyperbolic shape of the %sat vs. pO₂ graph for myoglobin (Mb) reflects its high oxygen affinity and positive cooperativity. This unique binding behavior is essential for the efficient uptake and release of oxygen in muscle tissues, where myoglobin acts as a molecular reservoir for oxygen, ensuring a steady supply to meet the demands of active muscles during periods of increased metabolic activity.