"Chitin" - what is it, definition of the term
A β‑(1→4) linked polymer of N‑acetylglucosamine, this structural polysaccharide forms the rigid component of the exoskeletons of arthropods such as ticks, insects, lice, and fleas; it is synthesized by chitin synthase enzymes, confers mechanical strength, and resists enzymatic degradation, serving as the primary material of their cuticular layers.
Detailed information
The β‑(1→4) linked N‑acetylglucosamine polymer forms a major structural component of the outer shell of many arthropods. Its linear chains arrange into crystalline microfibrils that interlock with protein matrices, creating a composite material that resists mechanical stress and desiccation.
Chemical analysis shows a repeating disaccharide unit, each bearing an acetyl group that reduces hydrogen‑bonding potential relative to cellulose. Crystallinity varies from α‑type, found in most insects, to β‑type, observed in certain crustaceans. Molecular weight ranges from a few hundred thousand to several million daltons, influencing solubility and enzymatic susceptibility.
Synthesis proceeds via membrane‑bound chitin synthases that polymerize UDP‑N‑acetylglucosamine. Gene families encode isoforms with distinct expression patterns during growth cycles. Regulation involves phosphorylation of the synthase complex and feedback inhibition by accumulated polymer.
In ticks, true bugs, lice, and fleas, the polymer reinforces the cuticle that encases each molt. During ecdysis, specialized enzymes degrade the existing layer, allowing expansion before a new, thicker sheet is deposited. The resulting exoskeleton provides protection against predators, environmental extremes, and host immune responses.
Mechanical testing reveals high tensile strength and low elasticity, attributes derived from the ordered arrangement of fibrils and cross‑linking with cuticular proteins. The polymer resists hydrolytic attack but is vulnerable to chitinolytic enzymes produced by pathogenic fungi and bacteria, a fact exploited in biological control strategies.
Derived derivatives serve multiple applied purposes:
- Deacetylated product employed as a biodegradable film for wound dressings.
- Nanofibers incorporated into agricultural coatings for controlled release of pesticides.
- Hydrogels used in drug delivery systems due to their swelling capacity and biocompatibility.
Research continues to explore genetic manipulation of synthase genes to alter exoskeletal properties, aiming to reduce vector competence of disease‑carrying species.