In the case of radioactive decay, this model describes exactly what is going on physically. In the case of ligand binding, the model may be a simplification. The model considers that all receptors are either free or bound to ligand. In fact, binding is a complicated process with multiple points of contact between ligand and receptor, so there must be some states of partial binding. Even though the model is simplified, it predicts experimental data very well.
Few models describe a physical process exactly.
Models that simplify the true molecular or physiological mechanisms can be very useful, so long as they are not too simple. Example model 3. When a ligand interacts with a receptor, or when a substrate interacts with an enzyme, the binding follows the law of mass action. In the case of enzyme kinetics, R is the enzyme and L is the substrate. The rate of RL formation equals R .