And this leads us into these two models. So these two models are generally used to basically describe the way that the binding between the substrate and the active side of the enzyme actually takes place. And although we still use the lock and key model, it's really the induced fifth model that describes more correctly the way that our binding takes place. So let's begin by discussing what we mean by the lock and key model. So lock and key simply means we have a key, we have a lock. And essentially when we place the key into the lock, we know that the shapes are complementary and that's why we have a perfect fit between our lock and between our keys.