And by the way, the major difference between these different proteases is the presence of a specific type of residue inside the active side of that enzyme. So in the case of seren proteasis from the name you might guess that inside that active side it's a serene molecule, a serine amino acid that plays the nucleochilic role of nucleophilically attacking or breaking that peptide bond. And so it's the serine that ultimately catalyzes that reaction. Now in addition to that serene, as we'll see in the next lecture, there are other additional residues present in the active side that also assist in the catalysis process as we'll discuss in the next lecture. Now, what are some examples of senior proteases and what are some of their roles? So let's begin with some digestive enzymes.