So this connects to this carbon that kicks off this terminal dalanine and that forms the green cross linkage between this terminal glycine on the pentaglycine molecule and this dalanine. The second carbon, the second D alanine, the carbon of that second D alanine. So this is the reaction that takes place, that forms the cross linkages inside bacterial cells. 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.