Chitin
Encyclopedia
Polymer
A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...
of a N-acetylglucosamine
N-Acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
, a derivative of glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, and is found in many places throughout the natural world. It is the main component of the cell wall
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
s of fungi, the exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
s of arthropod
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s such as crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s (e.g., crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s and shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
s) and insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, the radula
Radula
The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...
s of mollusks, and the beaks of cephalopods, including squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
es. In terms of structure, chitin may be compared to the polysaccharide cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
and, in terms of function, to the protein keratin
Keratin
Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...
. Chitin has also proven useful for several medical and industrial purposes.
The structure of chitin was solved by Albert Hofmann
Albert Hofmann
Albert Hofmann was a Swiss scientist known best for being the first person to synthesize, ingest and learn of the psychedelic effects of lysergic acid diethylamide . He authored more than 100 scientific articles and a number of books, including LSD: My Problem Child...
for which he received his doctorate.
Etymology
The English word "chitin" comes from the FrenchFrench language
French is a Romance language spoken as a first language in France, the Romandy region in Switzerland, Wallonia and Brussels in Belgium, Monaco, the regions of Quebec and Acadia in Canada, and by various communities elsewhere. Second-language speakers of French are distributed throughout many parts...
word chitine, which first appeared in 1836. These words were derived from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word chitōn, meaning mollusk, that is, influenced by the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
word khitōn
Chiton (costume)
A chiton was a form of clothing worn by men and women in Ancient Greece, from the Archaic period to the Hellenistic period ....
, meaning "tunic
Tunic
A tunic is any of several types of clothing for the body, of various lengths reaching from the shoulders to somewhere between the hips and the ankles...
" or "frock
Frock
Frock has been used since Middle English as the name for an article of clothing for men and women .- History of the frock :...
". That word may come from the Central Semitic
Semitic
In linguistics and ethnology, Semitic was first used to refer to a language family of largely Middle Eastern origin, now called the Semitic languages...
word *kittan, the Akkadian
Akkadian language
Akkadian is an extinct Semitic language that was spoken in ancient Mesopotamia. The earliest attested Semitic language, it used the cuneiform writing system derived ultimately from ancient Sumerian, an unrelated language isolate...
words kitû or kita’um, meaning flax
Flax
Flax is a member of the genus Linum in the family Linaceae. It is native to the region extending from the eastern Mediterranean to India and was probably first domesticated in the Fertile Crescent...
or linen
Linen
Linen is a textile made from the fibers of the flax plant, Linum usitatissimum. Linen is labor-intensive to manufacture, but when it is made into garments, it is valued for its exceptional coolness and freshness in hot weather....
, and the Sumerian
Sumerian language
Sumerian is the language of ancient Sumer, which was spoken in southern Mesopotamia since at least the 4th millennium BC. During the 3rd millennium BC, there developed a very intimate cultural symbiosis between the Sumerians and the Akkadians, which included widespread bilingualism...
word gada or gida.
A similar word, "chiton", refers to a marine animal with a protective shell (also known as a "sea cradle").
Chemistry, physical properties and biological function
Chitin is a modified polysaccharidePolysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
that contains nitrogen; it is synthesized
Biosynthesis
Biosynthesis is an enzyme-catalyzed process in cells of living organisms by which substrates are converted to more complex products. The biosynthesis process often consists of several enzymatic steps in which the product of one step is used as substrate in the following step...
from units of N-acetylglucosamine
N-Acetylglucosamine
N-Acetylglucosamine is a monosaccharide derivative of glucose. It is an amide between glucosamine and acetic acid...
(to be precise, 2-(acetylamino)-2-deoxy-D-glucose). These units form covalent β-1,4 linkages (similar to the linkages between glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
units forming cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
). Therefore, chitin may be described as cellulose
Cellulose
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to over ten thousand β linked D-glucose units....
with one hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
group on each monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
substituted with an acetyl
Acetyl
In organic chemistry, acetyl is a functional group, the acyl with chemical formula COCH3. It is sometimes represented by the symbol Ac . The acetyl group contains a methyl group single-bonded to a carbonyl...
amine
Amine
Amines are organic compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines,...
group. This allows for increased hydrogen bonding between adjacent polymers, giving the chitin-polymer matrix increased strength.
Arthropod
An arthropod is an invertebrate animal having an exoskeleton , a segmented body, and jointed appendages. Arthropods are members of the phylum Arthropoda , and include the insects, arachnids, crustaceans, and others...
s, however, it is often modified, becoming embedded in sclerotin
Sclerotin
Sclerotin is a component of the cuticles of various Arthropoda, most particularly insects. It is formed by cross-linking members of particular classes of protein molecules, a biochemical process called sclerotization, but technically. The resulting material adds physical stiffness to the toughness...
, a tanned protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
aceous matrix, which forms much of the exoskeleton
Exoskeleton
An exoskeleton is the external skeleton that supports and protects an animal's body, in contrast to the internal skeleton of, for example, a human. In popular usage, some of the larger kinds of exoskeletons are known as "shells". Examples of exoskeleton animals include insects such as grasshoppers...
. In its pure form, chitin is leathery, but in most invertebrates it occurs largely as a component of composite material
Composite material
Composite materials, often shortened to composites or called composition materials, are engineered or naturally occurring materials made from two or more constituent materials with significantly different physical or chemical properties which remain separate and distinct at the macroscopic or...
s. Combined with say, calcium carbonate
Calcium carbonate
Calcium carbonate is a chemical compound with the formula CaCO3. It is a common substance found in rocks in all parts of the world, and is the main component of shells of marine organisms, snails, coal balls, pearls, and eggshells. Calcium carbonate is the active ingredient in agricultural lime,...
, as in the shells of Crustacea
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
, it produces a much stronger composite, harder and stiffer than pure chitin, tougher than the mineral substance alone. Another difference between pure and composite forms can be seen by comparing the flexible body wall between the segments of a caterpillar
Caterpillar
Caterpillars are the larval form of members of the order Lepidoptera . They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture...
(mainly chitin) to the stiff, light elytron
Elytron
An elytron is a modified, hardened forewing of certain insect orders, notably beetles and a few of the true bugs ; in most true bugs, the forewings are instead called hemelytra, as only the basal half is thickened while the apex is membranous...
of a beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
(containing a large proportion of sclerotin).
Fossil record
Chitin was present in the exoskeletons of CambrianCambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
arthropods such as trilobite
Trilobite
Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
s. The oldest preserved chitin dates to the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, about .
Agriculture
Most recent studies point out that chitin is a good inducer for defense mechanismsPlant defense against herbivory
Plant defense against herbivory or host-plant resistance describes a range of adaptations evolved by plants which improve their survival and reproduction by reducing the impact of herbivores. Plants use several strategies to defend against damage caused by herbivores...
in plants. It has also been assessed as a fertilizer
Fertilizer
Fertilizer is any organic or inorganic material of natural or synthetic origin that is added to a soil to supply one or more plant nutrients essential to the growth of plants. A recent assessment found that about 40 to 60% of crop yields are attributable to commercial fertilizer use...
that can improve overall crop yields.
The EPA regulates chitin for agricultural use within the USA. Chitosan
Chitosan
Chitosan is a linear polysaccharide composed of randomly distributed β--linked D-glucosamine and N-acetyl-D-glucosamine...
is prepared from chitin by deacetylation.
Industrial
Chitin is used in industry in many processes. It is used as an additive to thicken and stabilize foods and pharmaceuticals. It also acts as a binder in dyeDye
A dye is a colored substance that has an affinity to the substrate to which it is being applied. The dye is generally applied in an aqueous solution, and requires a mordant to improve the fastness of the dye on the fiber....
s, fabric
Fabric
A fabric is a textile material, short for "textile fabric".Fabric may also refer to:*Fabric , the spatial and geometric configuration of elements within a rock*Fabric , a nightclub in London, England...
s, and adhesive
Adhesive
An adhesive, or glue, is a mixture in a liquid or semi-liquid state that adheres or bonds items together. Adhesives may come from either natural or synthetic sources. The types of materials that can be bonded are vast but they are especially useful for bonding thin materials...
s. Industrial separation membranes
Reverse osmosis
Reverse osmosis is a membrane technical filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on the pressurized side of the membrane and...
and ion-exchange resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
s can be made from chitin. Processes to size
Sizing
Sizing or size is any one of numerous specific substances that is applied to or incorporated in other material, especially papers and textiles, to act as a protecting filler or glaze....
and strengthen paper
Paper
Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....
employ chitin.
Medicine
Chitin's properties as a flexible and strongTensile strength
Ultimate tensile strength , often shortened to tensile strength or ultimate strength, is the maximum stress that a material can withstand while being stretched or pulled before necking, which is when the specimen's cross-section starts to significantly contract...
material make it favorable as surgical thread. Its biodegradibility
Biodegradation
Biodegradation or biotic degradation or biotic decomposition is the chemical dissolution of materials by bacteria or other biological means...
means it wears away with time as the wound heals. Moreover, chitin has some unusual properties that accelerate healing of wounds in humans.
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. To be specific, mice treated with chitin develop an allergic response, characterized by a build-up of interleukin-4, expressing innate immune cells. In these treated mice, additional treatment with a chitinase enzyme abolishes the response.
See also
- BiopesticideBiopesticideBiopesticides include "naturally occurring substances that control pests , microorganisms that control pests , and pesticidal substances produced by plants containing added genetic material or PIPs."Biopesticides are biochemical pesticides that are naturally occurring substances that control pests...
- ChitobioseChitobioseChitobiose is a dimer of β-1,4-linked glucosamine units. There is ambiguity as to which structure the name refers, owing to the method by which it was first isolated....
- ChitosanChitosanChitosan is a linear polysaccharide composed of randomly distributed β--linked D-glucosamine and N-acetyl-D-glucosamine...
(natural biocontrol for agricultural and horticultural uses) - LoricaLorica (biology)In biology, a lorica is a shell-like protective outer covering, often reinforced with sand grains and other particles that some protozoans and loricifera metazoans secrete. Usually it is tubular or conical in shape, with a loose case that is closed at one end. An example is the protozoan genus...
- SporopolleninSporopolleninthumb|right|270px|[[Scanning electron microscope|SEM]] image of pollen grainsSporopollenin is a major component of the tough outer walls of spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments...
- TectinTectin (secretion)Tectin is an organic substance secreted by certain ciliate protozoans. Tectin may form an adhesive stalk, disc or other sticky secretion. Tectin may also form a gelatinous envelope or membrane enclosing some ciliates as a protective capsule or lorica. Tectin is also called pseudochitin...