So we have aspiration, methylation glycosylation, we have proteol lysis, we have nacetilation as well as lipidation. So let's begin with the process of phosphorylation. So phosphorylation is the addition of a phosphate group onto certain amino acids, usually the serine, three anine and our tyrosine, on our polypeptide chain. And the enzyme that basically catalyzes the addition of the phosphate group is known as protein kinases. So by adding our phosphate group onto our polypeptide chain, we're basically increasing the hydrophilic character of that protein. And as we'll see in a future lecture, this type of modification is usually used in the process of the cell cycle, in the cell growth process, as well as signal transduction.