And before they are activated, they have to undergo many different types of processes, many different types of modifications. And together all these modifications are known as posttranslational modifications of our polypeptide chains. Now the types of posttranslational modifications that we're going to briefly discuss in this lecture are shown on the board. 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.