Chitin is a linear homopolymer of N-acetyl-β-D-glucosamine residues linked by β-1,4 glycosidic bonds. It is a major structural component of D. melanogaster exoskeleton, tracheal and internal tendon cuticles, and the intestinal peritrophic matrix. Chitin polymerisation is initiated in the cytosol by plasma membrane chitin synthase (CHS). The nascent chitin polymer is then translocated through the CHS translocating channel across the membrane and released into the extracellular space where it spontaneously assembles to form microfibrils. kkv mediates chitin synthesis in epidermal and tracheal cells while Chs2 synthetizes peritrophic matrix chitin in midgut cells. Chitin can be partially deacetylated which modulates the physical properties of chitin-containing structures. (Adapted from PMID:38072083 and PMID:26982439.)