Final answer:
The connection between affinity (Kd) and Km is that affinity is inversely proportional to Km. A lower Km indicates higher affinity, and a higher Km indicates lower affinity.
Step-by-step explanation:
Connection Between Affinity (Kd) and Km
The connection between affinity, often represented by the dissociation constant Kd, and the Michaelis constant (Km) can be complex because they pertain to different aspects of enzyme kinetics and ligand binding. Affinity (Kd) refers to the strength with which a ligand binds to its receptor or an enzyme substrate complex, while Km is a parameter of the Michaelis-Menten equation that represents the substrate concentration at which an enzyme operates at half of its maximum velocity (Vmax).
Answering the student's question, the correct option would be A) Affinity is inversely proportional to Km. This is because a lower Km value indicates a higher affinity for the substrate as the enzyme reaches half of its maximum velocity at a lower substrate concentration, suggesting a tighter binding. Conversely, a higher Km indicates a lower affinity because more substrate is needed to reach half of the Vmax.