Chitin (C8H13O5N)n (IPA: [ˈkaɪtn̩]) is a long-chain
polymer of beta-glucose that forms a hard, semitransparent
material found throughout the natural world. It is the main component of the cell walls of
fungi, the exoskeletons of arthropods, such as crustaceans (e.g. crab,
lobster and shrimp) and insects
(e.g. ants, beetles and butterflies), the radula of molluscs and the
beaks of cephalopods (e.g. squid, and octopuses). Chitin has also proven useful for several medical and industrial purposes.
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.
A
cicada sheds its chitinous exoskeleton.
In its unmodified form, chitin is translucent, pliable, resilient and quite tough. In arthropods, however, it is often modified, becoming embedded in a hardened proteinaceous matrix, which forms much of the exoskeleton. In its pure form
it's leathery, but when encrusted in calcium carbonate it becomes much harder.[1] 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
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.
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".[2]
A similar word, "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
Chitin's properties as a flexible and strong material make it favourable as
surgical thread. Its biodegradibility means it wears away
with time as the wound heals. Moreover, chitin has some unusual properties that accelerate healing of wounds in humans. Chitin has even been used as a stand-alone wound-healing agent. [3] 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.
Agriculture
Most recent studies point out that chitin is a good inductor for defense
mechanisms in plants.[citation needed] 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
- ^ Campbell, N. A. (1996) Biology (4th edition)
Benjamin Cummings, New Work. p.69 ISBN 0-8053-1957-3
- ^ American Heritage dictionary of the English Language: Fourth Edition. 2000. entry for chiton
- ^ http://www.halosource.com/licoppstechnology.asp
External links
be-x-old:Хіцін
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