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. So this is basically the diagram that describes the locking key. So we can basically imagine that the enzyme has this active side that is a perfect fit for this substrate in the same way that our lock is a perfect fit for our key. And when we place that key into our lock the key nor the lock actually changes in shape.