Now generally speaking, in covalent modification what happens is we actually transfer a functional group, a functional amid from one molecule onto that target enzyme that target protein. So we actually covalently attach a group onto that enzyme and that's precisely what changes the activity of that enzyme or the functionality of that protein. It can either turn on or in some cases turn off the activity of that enzyme. Now there are many different types of covalent modifications that can take place inside our cells. So we can modify the proteins in many different ways. For instance, we have processes like methylation acetylation, sulfination and many others that we're going to discuss in future lectures.