We have the lock and key model as well as the induced fit model. Now the induced fit model is the model is the theory that basically is accepted nowadays while the lock and key model is the older model that is basically no longer really accepted. And we'll see why that's the case in just a moment. So let's begin with the locking key model. This model presumes that the enzymes active side is a perfect keyhole for our substrate which is basically the key. So it states that the active side is a perfect fit for the substrate and neither the substrate nor the enzyme actually changes shape during our binding.