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. But the one that we're going to focus on is known as phosphorylation. And phosphorylation is a very common method of covalent modification. It's a very common method by which we actually control the activity of enzymes and change the functionality of proteins.