Chitin
Chitin is one of the main components in the cell walls of
fungi, the
exoskeleton of
insects and other
arthropods, and in some other animals. It is a
polysaccharide, made out of units of acetylglucosamine (more completely, N-acetyl-D-glucos-2-amine). These are linked together in β-1,4 fashion, the same as the
glucose units that make up
cellulose. So chitin may be thought of as
cellulose, with one
hydroxyl group on each
monomer replaced by an
acetylamino group. This allows for increased
hydrogen bonding between adjacent
polymers, giving the material increased strength.
"Chitin" and "chiton" (a marine animal) both derive from the same Greek word meaning "tunic", referring to the hardness.