The next reaction leads to formation of the activated sugar UDP-N-acetyl-α-D-glucosamine. This activated sugar also participates in the eukaryotic N-linked glycosylation pathway (see pathway protein N-glycosylation (eukaryotic, high mannose)). The final step in chitin biosynthesis utilizes UDP-N-acetyl-α-D-glucosamine in a polymerization reaction to form chitin, catalyzed by chitin synthase. The chitin synthase reaction occurs in specialized microdomains of the plasma membrane. Chitin synthase is an integral membrane protein complex that polymerizes and extrudes chitin.