Secondary metabolites, distinction

Pulmonates are air-breathing molluscs that do not include many families and genera [68]. Siphonaria species from many distinct geographical areas possess a series of secondary metabolites with polypropionate skeletons characterized by the presence of ketal, pyrone and furanone moieties [47]. A rigorous biosynthetic experiment [69] proved that Siphonaria denticulata is able to... 

Expressed sequence tag (EST) analysis of cDNAs from specific plant tissues has proved to be a valuable tool for the identification of genes for secondary metabolite biosynthesis.36 We have used this approach to identify two distinct sequences predicted to encode OSCs from cDNA libraries from roots of diploid oat (Avena strigosa).35 One of these sequences is highly homologous to cycloartenol... 

Perhaps most conspicuous by their absence from the list (cf. Table VIII) are the alkaloids. These substances, generally defined as nitrogen-containing secondary metabolites, are common plant products and usually have distinct physiological activities. Nevertheless, to date no reports seem to have appeared concerning the presence (or absence) of alkaloids as Gossypium metabolites. 

Wessels M, Konig GM, Wright AD (2000) New Natural Product Isolation and Comparison of the Secondary Metabolite Content of Three Distinct Samples of the Sea Hare Aplysia dactylomela from Tenerife. J Nat Prod 63 920... 

This review will compare the strategies taken by synthetic chemists to produce natural products with the strategies utilized by nature. What types of molecular scaffolds are made in each case in the process of assembling a natural product Rarely will the paths be identical, but are there features that reveal a more universal logic in the construction of these molecules Or, by contrast, are there fundamental distinctions between organic synthesis and biosynthesis To answer these questions we have chosen - from a biosynthetic point of view - a diverse selection of secondary metabolites, ranging from relatively simple terpenes and shikimate-derived... 

A distinction needs to be made between allocation of resources and the translocation of previously synthesized components. An increase in the concentration of secondary metabolites as a result of increased synthesis represents a change in allocation to defenses. In contrast, an increase in the concentration of secondary metabolites as a result of translocation does not represent an increased allocation to defenses as far as synthesis is concerned, though there could be increased allocation to transporting costs (see above). Rather, translocation represents a rearrangement of prior allocations, as an increase in metabolite concentrations at the sink is balanced by a decrease of metabolite concentrations at the source the amount of metabolite in the whole organism remains unchanged. 

These defense compounds are better known as natural products or secondary metabolites. The latter expression originally meant compounds which are not essential for life, and thus distinct from primary metabolites 34,35,38). Unfortunately the term secondary has also a pejorative meaning, indicating perhaps that the compounds have no importance for the plant. As discussed in this chapter, just the opposite is true. 

It is well known that the secondary metabolites of grapes provide the basis of varietal character in wine. The important secondary metabolites are represented by several groups of compounds that contribute to the distinctive aroma profile of wines made from particular varieties of Vitis vinifera. They include terpenes, Ci3-norisoprenoids, aliphatics, benzene-derivatives, volatile phenols and long-chain polyfuntional thiols. While constituent aroma compounds within these groups occur in most grape varieties, it is only when one or more of these compounds occur at concentrations well above their odour threshold that a distinctive varietal aroma emerges. 

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