Chitin
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[[Image:Chitin fixed.png|thumb|right|Structure of the chitin [[molecule]], showing two of the [[N-Acetylglucosamine]] units that repeat to form long chains in beta-1,4 linkage.]]
'''Chitin''' ([[carbon|C]]<sub>8</sub>[[hydrogen|H]]<sub>13</sub>[[oxygen|O]]<sub>5</sub>[[nitrogen|N]])<sub>n</sub> ({{pronEng|ˈkaɪtən}}) is a long-chain [[polymer]] of a N-acetylglucosamine, a derivative of glucose, and it is found in many places throughout the natural world. It is the main component of the [[cell wall]]s of [[fungi]], the [[exoskeleton]]s of [[arthropod]]s, such as [[crustacean]]s (like the [[crab]], [[lobster]] and [[shrimp]]) and the [[insect]]s, including [[ants]], [[beetles]] and [[butterflies]], the [[radula]] of [[mollusk]]s and the beaks of the [[cephalopods]], including [[squid]] and [[octopus]]es. 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 [[biosynthesis|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 [[acetyl]][[amine]] group. This allows for increased [[hydrogen bonding]] between adjacent [[polymers]], giving the chitin-polymer matrix increased strength.
[[Image:Lyristes plebejus.jpg|thumb|right|A [[cicada]] sheds its chitinous exoskeleton.]]
In its unmodified form, chitin is translucent, pliable, resilient and quite tough. In [[arthropod]]s, however, it is often modified, becoming embedded in a hardened [[protein]]aceous matrix, which forms much of the [[exoskeleton]]. In its pure form it is leathery, but when encrusted in [[calcium carbonate]] it becomes much harder.<ref name=Campbell>Campbell, N. A. (1996) ''Biology'' (4th edition) Benjamin Cummings, New Work. p.69 ISBN 0-8053-1957-3</ref> The difference between the unmodified and modified forms can be seen by comparing the body wall of a [[caterpillar]] (unmodified) to a [[beetle]] (modified).
Chitin is one of many naturally occurring [[polymers]]. Its breakdown may be catalyzed by [[enzyme]]s called [[chitinase]]s, secreted by microorganisms such as [[bacteria]] and [[fungi]], and produced by some plants. Some of these microorganisms have [[Chemoreceptors|receptors]] to simple [[sugars]] from the decomposition of chitin. If chitin is detected, they then produce enzymes to digest it by cleaving the [[glycosidic bond]]s 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.
== Etymology==
The English word "chitin" comes from the [[French language|French]] word "chitine", which first appeared in 1836. These words were derived from the [[Latin language|Latin]] word "chitōn", meaning [[mollusk]]. That is either influenced by, or related to the [[Greek language|Greek]] word ''[[chiton (costume)|khitōn]]'', meaning "[[tunic]]" or "[[frock]]", the Central [[Semitic]] word "*kittan", the [[Akkadian language|Akkadian]] words "kitû" or "kita’um", meaning [[flax]] or [[linen]], and the [[Sumerian language|Sumerian]] word "gada" or "gida".<ref>[http://bartelby.com/61/7/C0310700.html American Heritage dictionary of the English Language: Fourth Edition. 2000. entry for chiton]</ref>
A similar word, "[[Chiton#Name|chiton]]", refers to a marine animal with a protective shell (also known as a "sea cradle").
== Uses ==
=== Industrial ===
Chitin is used industrially in many processes. It is used in [[water purification]], and as an additive to thicken and stabilize foods and pharmaceuticals. It also acts as a binder in dyes, fabrics, and adhesives. Industrial separation membranes and ion-exchange resins can be made from chitin. Processes to size and strengthen paper employ chitin.
=== Medicine ===
{{Citecheck|date=July 2008}}
Chitin's properties as a flexible and [[tensile strength|strong]] material make it favourable as [[Suture|surgical thread]]. Its [[biodegradation|biodegradibility]] means it wears away with time as the wound heals. Moreover, chitin has some unusual properties that accelerate healing of wounds in [[human]]s. Chitin has even been used as a stand-alone wound-healing agent. <ref>[http://www.halosource.com/licoppstechnology.asp Welcome to HaloSource, Inc. - Antimicrobial & Clean Technology Solutions<!-- Bot generated title -->]</ref> Chitin is used to make [[Chitosan]], a product with numerous commercial and possible biomedical uses. Its most famous use is as a weight loss product.
Occupations associated with high environmental chitin levels, such as shellfish processors, are prone to high incidences of asthma. Recent studies have suggested that chitin may play a role in a possible pathway in human allergic disease. Specifically, mice treated with chitin develop an allergic response, characterized by a build-up of interleukin-4 expressing innate immune cells. Treatment with a chitinase enzyme abolishes the response. [http://www.nature.com/nature/journal/v447/n7140/edsumm/e070503-13.html]
=== Agriculture ===
Most recent studies point out that chitin is a good inductor for [[plant defense against herbivory|defense mechanisms]] in plants.{{Fact|date=August 2007}} It was recently tested as a [[fertilizer]] that can help plants develop healthy [[immune]] responses, and have a much better yield and life expectancy.
== References ==
<references/>
* Martín-Gil FJ, Leal JA, Gómez-Miranda B, Martín-Gil J, Prieto A, Ramos-Sánchez MC. "Low temperature thermal behaviour of chitins and chitin-glucans". ''Thermochim. Acta'', 1992, vol. 211, pp. 241-254
== External links ==
* [http://www.greatvistachemicals.com/biochemicals/chitin.html Chitin Product Information from China GreatVista Chemicals]
* [http://www.ocean.udel.edu/horseshoecrab/Research/chitin.html Horseshoe Crab Chitin Research]
* {{MeshName|Chitin}}
{{carbohydrates}}
[[Category:Biomolecules]]
[[Category:Polysaccharides]]
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