This is what the blue curve actually describes. So to see this in equation form, let's take a look at the following equation. This equation basically describes what has taken place inside that beaker once we add the substrate. So initially we have the enzyme by itself and then we add the substrate and the substrate is also by itself. But then what begins to happen is the substrate begins to bind onto that enzymes active site and we form an intermediate molecule known as the enzyme substrate complex. Now going this way the rate constant is k one, but once we form some of this complex it begins to dissociate back into these two reactants and the rate constant of that reverse reaction is K minus one, at the same time some of that complex.