Exoskeletons

Insect Growth Regulators. These compounds (40—45), unlike most conventional insecticides, interfere with biochemical processes that are unique to arthropods eg, molting, ecdysis, and formation of the chitinous exoskeleton. Therefore, they are selective insecticides with very low mammalian toxicity. 

Plant stmctural material is the polysaccharide cellulose, which is a linear P (1 — 4) linked polymer. Some stmctural polysaccharides iacorporate nitrogen iato thek molecular stmcture an example is chitin, the material which comprises the hard exoskeletons of kisects and cmstaceans. Chitki is a cellulose derivative whereki the OH at C-2 is replaced by an acetylated amino group (—NHCOCH ). Microbial polysaccharides, of which the capsular or extracellular (exopolysaccharides) are probably the most important class, show more diversity both ki monomer units and the nature of thek linkages. 

A major biological sink for CO9 that is often overlooked is the calcium carbonate shells of corals, molluscs, and Crustacea. These invertebrate animals deposit CaCOa in the form of protective exoskeletons. In some invertebrates, such as the sderaetinians (hard corals) of tropical seas, photosynthetic dinoflagellates (kingdom Protoctista) known as zooxanthellae live within the ani-... 

Fig. 14.20). Magnesium occurs in seawater and as the mineral dolomite, CaCOyMgCO,. Calcium also occurs as CaCO in compressed deposits of the shells of ancient marine organisms and exoskeletons of tiny one-celled organisms these deposits include limestone, calcite, and chalk (a softer variety of calcium carbonate). 

Caterpillars and other moulting insects excrete the hormone a-ecdysone which at moulting time becomes hydroxylated to 20-hydroxyecdysone (20-E), which in turn triggers the moulting process enabling the insect to shed its exoskeleton and resume feeding. Rohm and Hass have developed a novel insecticide, tebufenozide (Formula 9.5) which mimics 20-E, binding to the same site. The consequence of this is that the insect stops... 

Glucose molecules can link together into chains, with each ring tethered to the next by a bridging oxygen atom. In one form, this is cellulose, the stiff material that gives the stalks of plants and the trunks of trees their structural strength. Chitin, a variation on cellulose, is an even stiffen material that forms the exoskeletons of crustaceans such as crabs and lobsters. 

Bierkens J, Vangenechten JHD, Van Puymbroeck S, et al. 1986. Effect of Al and humic acids on the 241Am adsorption on the exoskeleton of the crayfish Astacus leptodactylus eschscholtz. Health Phys 50(2) 277-280. 

Shell, coral, pearl (exoskeletons Limestone and/or Calcium carbonate... 

Shell is the term generally used to refer to the hard exoskeleton of some animals, such as the mollusks, as well as to the protective covering of the eggs of birds and some amphibians and reptiles. The shell of many mollusks, for example, consists of three layers the innermost is a shiny layer of nacre, also known as mother of pearl, which includes a mixture of the mineral arag-... 

Winter, A.D. and Page, A.P. (2000) Prolyl 4-hydroxylase is an essential procollagen modifying enzyme required for exoskeleton formation and the maintenance of body shape in the nematode Caenorhabditis elegans. Molecular and Cellular Biology 20, 4084-4093. 

Calcium Carbonate CaC03 Calcite Aragonite Vaterite Widespread in animals and plants Exoskeleton Gravity, Ca store Eye lens... 

Sugawara, A., Nishimura, T., Yamamoto, Y., Inoue, H., Nagasawa, H. and Kato, T. (2006) Self-organization of oriented calcium carbonate/polymer composites effects of a matrix peptide isolated from the exoskeleton of a crayfish. Angewandte Chemie International Edition, 45, 2876-2879. 

Calcium carbonate (calcite, aragonite, Exoskeletons (mollusc and egg shells ... 

Strontium sulphate (celestite) Exoskeletons of a few marine organisms... 

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