Final answer:
In the context of ligand binding, occupancy (theta) is the fraction of total binding sites that are occupied. It is calculated by dividing the number of occupied binding sites by the total number of binding sites.
Step-by-step explanation:
Occupancy (theta) is defined in the context of ligand binding to a set of receptors or substrate binding to enzymes. It represents the fraction of total binding sites that are occupied by a ligand or substrate. The formula to calculate occupancy is:
Occupancy (theta) = (Number of occupied binding sites) / (Total number of binding sites)
Therefore, the correct answer is:
a) All of the binding sites occupied/total binding sites
This is because occupancy is a measure of how many binding sites are occupied relative to the total number available, which can provide information about the binding affinity and the physiological efficacy of a ligand or drug.