Final answer:
Myoglobin can bind one molecule of O₂, while hemoglobin can bind four molecules of O₂, which is option a) Mb: 1, Hb: 4.
Step-by-step explanation:
Myoglobin (Mb) and hemoglobin (Hb) are both oxygen-binding proteins, but they differ in the number of oxygen molecules they can bind. Myoglobin has a single oxygen-binding site as it consists of only one heme group, and therefore, it can bind one molecule of oxygen. In contrast, hemoglobin consists of four subunits, each containing one heme group, enabling it to bind four oxygen molecules. Each iron ion in the heme can bind to one oxygen molecule, therefore, the correct answer to the question of how many molecules of O₂ myoglobin and hemoglobin can bind, respectively, is a) Mb: 1, Hb: 4. This is supported by the oxygen dissociation curves for these proteins, where myoglobin has a hyperbolic curve and hemoglobin has a sigmoidal, or S-shaped, curve indicating cooperative binding.