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 the D. melanogaster exoskeleton, tracheal and internal tendon cuticles, and the intestinal peritrophic matrix. Chitin degradation is mediated by chitinases, which cleave chitin at random positions producing chitooligosaccharides, and β-N- acetylglucosaminidases, which catalyze the stepwise removal of terminal, nonreducing β-N-acetylglucosamine residues from chitooligosaccharides. Chitin degradation occurs, for example, during D. melanogaster molting and cuticle turnover. (Adapted from PMID:26982439.)