Chitin (C₈H₁₃O₅N)_n ( ) is a long-chain polymer of a N-acetylglucosamine, a derivative of glucose, and is found in many places throughout the natural world. It is the main component of the cell walls of fungi, the exoskeletons of arthropods, such as crustaceans (e.g. crabs, lobsters and shrimps) and insects, including ants, beetles and butterflies, the radula of mollusks and the beaks of cephalopods, including squid and octopuses. Chitin has also proven useful for several medical and industrial purposes. Chitin is a biological substance which may be compared to the polysaccharide cellulose and to the protein keratin. Although keratin is a protein, and not a carbohydrate like chitin, both keratin and chitin have similar structural functions.

Chemistry, physical properties and biological function

Chitin is a polysaccharide; it is synthesized from units of N-acetylglucosamine (more completely, N-acetyl-D-glucos-2-amine). These units form covalent β-1,4 linkages (similar to the linkages between glucose units forming cellulose). Chitin may therefore be described as cellulose with one hydroxyl group on each monomer substituted with an acetylamine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength.

Chitin

Chitin is one of many naturally occurring polymers. It is one of the most abundant natural materials in the world. Over time it is bio-degradable in the natural environment. Its breakdown may be catalyzed by enzymes called chitinases, secreted by microorganisms such as bacteria and fungi, and produced by some plants. Some of these microorganisms have receptors to simple sugars from the decomposition of chitin. If chitin is detected, they then produce enzymes to digest it by cleaving the glycosidic bonds in order to convert it to simple sugars and ammonia.

Chemically, chitin is closely related to chitosan (a more water-soluble derivative of chitin). It is also closely related to cellulose in that it is a long unbranched chain of glucose derivatives. Both materials contribute structure and strength, protecting the organism.

Fossil record

for: taphonomy The oldest preserved chitin dates to the Oligocene, about ma: 25.

Etymology

The English word "chitin" comes from the French word "chitine", which first appeared in 1836. These words were derived from the Latin word "chitōn", meaning mollusk. That is either influenced by, or related to the Greek word khitōn, meaning "tunic" or "frock", the Central Semitic word "*kittan", the Akkadian words "kitû" or "kita'um", meaning flax or linen, and the Sumerian word "gada" or "gida".