Now, let's take a look at the reaction that is actually catalyzed by this type of enzyme. So what exactly does the reaction actually look like? So let's suppose we have a sugar and the sugar is basically shown in red. And what we want to do is we want to attach another sugar, let's say a glucose molecule, onto that red sugar. So this is the purple glucose that we want to attach onto that sugar molecule. Now, before the glycosyl transferase can actually catalyze this reaction, what we have to do is we have to activate this incoming glucose molecule.