Crustacean shells, parasite eggs, and fungal cell walls are just a few of the many places you can find the tough sugar molecule chitin . In terms of molecular structure, chitin, chitosan, and cellulose are all very similar to one another. Chitin is a naturally occurring polysaccharide that can be processed into chitosan by removing an acetyl group. Cellulose is an important structural component of plant cell walls. Chitin's chemical structure is very close to that of cellulose, the cell wall component of plants. Glucose is the fundamental building block of cellulose, whereas acetylglucosamine is the fundamental building block of chitin. A similar mechanism for virus transmission may be at work in the wheat mosaic virus, which combines chitin and cellulose.