And the enzyme that catalyzes speeds of this particular reaction inside bacterial cells is known as glycopeptide transpeptidase. So in bacterial cells, this cross linking is catalyzed by an enzyme we call glycopeptide transpeptidase. And if we examine the active site of this enzyme, the catalytic amino acid, the catalytic residue that catalyzes this reaction is serine. So let's focus on how this actually takes place inside the active side of this transpeptidase enzyme. So this is a portion of the active side and this is that catalytic residue, that Serene molecule. So what happens is we take this blue molecule that we have here that is basically attached to, let's say, the linear polysaccharide chain here.