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Chitin (carbon8hydrogen13oxygen5nitrogen)n ( ) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. It is a primary component of in fungi (especially filamentous and mushroom-forming fungi), the of such as crustaceans and insects, the , and gladii of and in some nematodes and diatoms. It is also synthesised by at least some fish and . Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry. The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.
A similar word, "chiton", refers to a marine animal with a protective shell.
Chitin is a modified polysaccharide that contains nitrogen; it is biosynthesis from units of N-acetyl-D-glucosamine (to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-(1→4)-linkages (like the linkages between glucose units forming cellulose). Therefore, chitin may be described as cellulose with one hydroxyl group on each monomer replaced with an acetyl amine group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength.
In its pure, unmodified form, chitin is translucent, pliable, resilient, and quite tough. In most , however, it is often modified, occurring largely as a component of composite materials, such as in sclerotin, a tanned matrix, which forms much of the exoskeleton of . Combined with calcium carbonate, as in the shells of and , chitin produces a much stronger composite. This composite material is much harder and stiffer than pure chitin, and is tougher and less brittle than pure calcium carbonate.Campbell, N. A. (1996) Biology (4th edition) Benjamin Cummings, New Work. p.69 Another difference between pure and composite forms can be seen by comparing the flexible body wall of a caterpillar (mainly chitin) to the stiff, light elytron of a beetle (containing a large proportion of sclerotin).
In butterfly wing scales, chitin is organized into stacks of constructed of chitin that produce various iridescent colors serving phenotype signaling and communication for mating and foraging. The elaborate chitin gyroid construction in butterfly wings creates a model of optical devices having potential for innovations in biomimicry. in the genus Cyphochilus also utilize chitin to form extremely thin scales (five to fifteen thick) that diffusely reflect white light. These scales are networks of randomly ordered filaments of chitin with diameters on the scale of hundreds of , which serve to scatter light. The multiple scattering of light is thought to play a role in the unusual whiteness of the scales. In addition, some social wasps, such as Protopolybia chartergoides, orally secrete material containing predominantly chitin to reinforce the outer nest envelopes, composed of paper.
Chitosan is produced commercially by deacetylation of chitin by treatment with sodium hydroxide. Chitosan has a wide range of biomedical applications including wound healing, drug delivery and tissue engineering. Due to its specific intermolecular hydrogen bonding network, dissolving chitin in water is very difficult. Chitosan (with a degree of deacetylation of more than ~28%), on the other hand, can be dissolved in dilute acidic aqueous solutions below a pH of 6.0 such as acetic, formic and lactic acids. Chitosan with a degree of deacetylation greater than ~49% is soluble in water
Chitin is sensed mostly in the lungs or gastrointestinal tract where it can activate the innate immune system through or , as well as an adaptive immune response through T helper cells. in skin can also react to chitin or chitin fragments.
Some pathogens produce chitin-binding proteins that mask the chitin they shed from these receptors. Zymoseptoria tritici is an example of a fungal pathogen that has such blocking proteins; it is a major pest in wheat crops.
Chitin and chitosan are under development as scaffolds in studies of how tissue grows and how Wound healing, and in efforts to invent better bandages, surgical suture, and materials for allotransplantation. Surgical suture made of chitin have been experimentally developed, but their lack of elasticity and problems making thread have prevented commercial success so far.
Chitosan has been demonstrated and proposed to make a reproducible form of biodegradable plastic. Chitin are extracted from crustacean waste and mushrooms for possible development of products in tissue engineering, drug delivery and medicine.
Chitin has been proposed for use in building structures, tools, and other solid objects from a composite material, combining chitin with Martian soil. To build this, the biopolymers in the chitin are suggested as the binder for the regolith aggregate to form a concrete-like composite material. The authors believe that waste materials from food production (e.g. scales from fish, exoskeletons from crustaceans and insects, etc.) could be put to use as feedstock for manufacturing processes.
Plants
Plants also have receptors that can cause a response to chitin, namely chitin elicitor receptor kinase 1 and chitin elicitor-binding protein. The first chitin receptor was cloned in 2006. When the receptors are activated by chitin, genes related to plant defense are expressed, and jasmonate hormones are activated, which in turn activate systemic defenses. Commensalism fungi have ways to interact with the host immune response that, , were not well understood.
Fossil record
Chitin was probably present in the exoskeletons of Cambrian arthropods such as . The oldest preserved (intact) chitin samples thus far reported are dated to the Oligocene, about , from specimens encased in amber where the chitin has not completely degraded.
Uses
Agriculture
Chitin is a good inducer of plant defense mechanisms for controlling plant disease. It has potential for use as a soil fertilizer or Soil conditioner to improve fertility and plant resilience that may enhance crop yields.
Industrial
Chitin is used in many industrial processes. Examples of the potential uses of chemically modified chitin in food processing include the formation of edible films and as an additive to thicken and stabilize foods and food emulsions. Processes to Sizing and strengthen paper employ chitin and chitosan.
Research
How chitin interacts with the immune system of plants and animals has been an active area of research, including the identity of key receptors with which chitin interacts, whether the size of chitin particles is relevant to the kind of immune response triggered, and mechanisms by which immune systems respond. Chitin is deacetylated chemically or enzymatically to produce chitosan, a highly Biocompatibility polymer which has found a wide range of applications in the biomedical industry. Chitin and chitosan have been explored as a vaccine adjuvant due to its ability to stimulate an immune response.
See also
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