Exoskeleton, of insects and crustaceans

Plant structural material is the polysaccharide cellulose, which is a linear p (1 —> 4) linked polymer. Some structural polysaccharides incorporate nitrogen into their molecular structure an example is chitin, the material which comprises the hard exoskeletons of insects and crustaceans. Chitin is a cellulose derivative wherein the OH at C-2 is replaced by an acetylated amino group (—NHCOCH3). Microbial polysaccharides, of which the capsular or extracellular (exopolysaccharides) are probably the most important class, show more diversity both in monomer units and the nature of their linkages. 

A jS-1,4 polymer of A-acetylglucosamine that lends strength and rigidity to the exoskeletons of insects and crustaceans, (p. 1139)... 

Like cellulose (O Sect. 3.1), chitin imparts mechanical strength. Both chitin and cellulose form fibrils. Chitin fibrils are structural elements in the exoskeletons of insects and crustaceans. Fungal cell walls, which often contain 80-90% (dry-weight basis, db) polysaccharide, have been categorized into eight types by polysaccharide composition ... 

Chitin. A homopolymer of the amino sugar, acetyl glucosamine acts as a structural component of the exoskeleton of insects and crustaceans. 

Chitin Animal (crustacean shells, exoskeletons of insects and other arthropods) microbial (fungal cell walls) a-(l/4)-linked N-acetyl-d-glucosamine residues. [39]... 

Chitin, identical in linkage to cellulose but composed of fV-acetylglucosamine instead of glucose, is the major structural component of insect and crustacean exoskeletons as well as a cell wall component of molds and fiingi. The structural comments regarding cellulose also apply generally to chitin, especially in terms of stability. Less industrial development has been done with this polymer, in part because shrimp shells may present a more difficult starting material than trees. 

Chitin synthase inhibitors are used commercially as insecticides because they preventthe formation of a new exoskeleton and the shedding of the old one. The insect becomes trapped in an old exoskeleton that cannot grow. These inhibitors are highly toxic to insects and crustaceans, but relatively nontoxic to mammals. The most common chitin synthase inhibitors are substituted benzoyl-ureas such as diflubenzuron, which was first registered as an insecticide in 1976. 

Chitosan is not widely present as such in nature and thus cannot be directly extracted from natural resources. Indeed, chitosan is a derivative of natural chitin, the second most abundant polysaccharide in nature after cellulose [2]. Typically, chitosan is obtained by deacetylation of the Ai-acetyl glucosamine units of chitin, generally by hydrolysis under alkali conditions at high temperature. The deacetylation of chitin is rarely complete. When the degree of acetylation falls below the value of 60 mol%, chitin becomes chitosan. In nature, chitin is present in life forms and more particularly in insects and crustaceans where it represents the major component of their exoskeleton. Chitin is also present in the cell wall of some mushrooms [7, 8]. Generally, chitosans produced from mushrooms present a narrow molecular weight distribution compared to chitosan produced from shrimps, and a non-animal source is considered to be safer for biomedical and healthcare uses. 

Chitosan is a linear copolymer composed of N-acetyl-D-glucosamine and D-glucosamine units [Fig. 16.4). It is derived from alkaline deacetylation of chitin that is the second most abundant polysaccharide next to cellulose [Fig. 16.4) [Sloan, 1992). Chitin is the main component in the shells of crustaceans such as shrimp, crab, and lobster. It is also found in the exoskeleton of mollusks and insects, and the cell walls of some fungi [Rlnaudo, 2008 Raabe et al., 2007 Vincent and Wegst, 2000). 

Chitin is a nitrogen-containing polysaccharide that forms the shells of crustaceans and the exoskeletons of insects. It is similar to cellulose, except that the hydroxyl group at C-2 of each glucose unit is replaced by an acetylamino group, CH3CONH—. 

Chitin is a natural polysaccharide including amino and acetyl groups [3]. Chitin is considered one of the most abxmdant natural polysaccharides on earth [96] and is found in species of lower plants and animals. It can be obtained from fungi, yeast, green, brown and red algae, as well as from insects and crustaceans. In insects and crustaceans, chitin is the main component of the exoskeleton [4]. It is composed of 2-acetamido-2-deoxy-(3-Dglucose... 

Chitin is a polysaccharide that has a structure very similar to that of cellulose and the bacterial cell wall polysaccharide murein. The structure of chitin is essentially the structure of cellulose, with the hydroxyl group at C-2 of the D-glucopyranose residue substituted with an A -acetylamino group [132] (see Fig. 6.15A). Chitin is the structural polysaccharide that replaces cellulose in the cell wall of many species of lower plants. It is found in fungi, yeast, green algae, and brown and red seaweed cell walls. Chitin is also the major component of the exoskeleton of insects. It is found in the cuticles of annelids, molluscs, and in the shells of crustaceans such as shrimp, crab, and lobster [133]. 

Along with cellulosic materials, chitosan is one of the most important natural products. It is the most important derivative of chitin. Chitosan is derived from different natural resources that include shellfish like shrimp, crabs, the exoskeletons of insects, arthropods such as crustacean shells, prawns beaks of cephalopods and cell walls of fungi (Shukla et al., 2013). Figure 1.8 shows the structure of chitin derived from the chitin. 

Chitin is a polysaccharide constituted of N -acctylglucosamine, which forms a hard, semitransparent biomaterial found throughout the natural world. Chitin is the main component of the exoskeletons of crabs, lobsters and shrimps. Chitin is also found also in insects (e.g. ants, beetles and butterflies), and cephalopods (e.g. squids and octopuses) and even in fungi. Nevertheless, the industrial source of chitin is mainly crustaceans. 

Chitin, which is the structural component of the exoskeleton of invertebrates such as crustaceans, insects, and spiders, resembles cellulose with the exception that the hydroxy groups on carbon 2 are replaced by acetylamino groups. 

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