Secondary metabolite

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Secondary metabolites are organic compounds that are not directly involved in the normal growth, development, or reproduction of an organism. Unlike primary metabolites, absence of secondary metabolites does not result in immediate death, but rather in long-term impairment of the organism's survivability, fecundity, or aesthetics, or perhaps in no significant change at all. Secondary metabolites are often restricted to a narrow set of species within a phylogenetic group. Secondary metabolites often play an important role in plant defense against herbivory and other interspecies defenses. Humans use secondary metabolites as medicines, flavorings, and recreational drugs.[1]

Secondary metabolites aid a plant in important functions such as protection, competition, and species interactions, but are not necessary for survival. One important defining quality of secondary metabolites is their specificity. Usually, secondary metabolites are specific to an individual species.[2] Research also shows that secondary metabolic can affect different species in varying ways. In the same forest, four separate species of arboreal marsupial folivores reacted differently to a secondary metabolite in eucalypts.[3] This shows that differing types of secondary metabolites can be the split between two herbivore ecological niches.[3] Additionally, certain species evolve to resist plant secondary metabolites and even use them for their own benefit. For example, monarch butterflies have evolved to be able to eat milkweed (Asclepias) despite the toxic secondary metabolite it contains.[4] This ability additionally allows the butterfly and caterpillar to be toxic to other predators due to the high concentration of secondary metabolites consumed.[4]

Human health implications[edit]

Most polyphenol nutraceuticals from plant origin must undergo intestinal transformations, by microbiota and enterocyte enzymes, in order to be absorbed at enterocyte and colonocyte levels. This gives rise to diverse beneficial effects in the consumer, including a vast array of protective effects against viruses, bacteria, and protozoan parasites.[5]

Secondary metabolites also have a strong impact on the food humans eat. Some researchers believe that certain secondary metabolite volatiles are responsible for human food preferences that may be evolutionarily based in nutritional food.[6] This area of interest has not been thoroughly researched, but has interesting implications for human preference. Many secondary metabolites aid the plant in gaining essential nutrients, such as nitrogen. For example, legumes use flavonoids to signal a symbiotic relationship with nitrogen fixing fungi (rhizobium) to increase their nitrogen uptake.[4] Therefore, many plants that utilize secondary metabolites are high in nutrients and advantageous for human consumption.

Categories[edit]

Most of the secondary metabolites of interest to humankind fit into categories which classify secondary metabolites based on their biosynthetic origin. Since secondary metabolites are often created by modified primary metabolite synthases, or "borrow" substrates of primary metabolite origin, these categories should not be interpreted as saying that all molecules in the category are secondary metabolites (for example the steroid category), but rather that there are secondary metabolites in these categories.

Small "small molecules"[edit]

Big "small molecules", produced by large, modular, "molecular factories"[edit]

Non-"small molecules" - DNA, RNA, ribosome, or polysaccharide "classical" biopolymers[edit]

See also[edit]

References[edit]

  1. ^ "Secondary metabolites - Knowledge Encyclopedia". www.biologyreference.com. Retrieved 2016-05-10. 
  2. ^ Pichersky, E. & Gang, D.R. (2000) Genetics and biochemistry of secondary metabolites in plants: an evolutionary perspective. Trends in plant science, 5, 439-445.
  3. ^ a b Jensen, L.M., Wallis, I.R., Marsh, K.J., Moore, B.D., Wiggins, N.L., & Foley, W.J. (2014) Four species of arboreal folivore show differential tolerance to a secondary metabolite. Oecologia, 176, 251-258.
  4. ^ a b c Croteau, R., Kutchan, T. M., & Lewis, N. G. (2000). Natural products (secondary metabolites). Biochemistry and molecular biology of plants, Ch. 24, 1250-1319.
  5. ^ http://www.hindawi.com/journals/bmri/2015/905215/
  6. ^ Goff, S.A. & Klee, H.J. (2006) Plant volatile compounds: sensory cues for health and nutritional values? Science, 311, 815-819.
  7. ^ Chizzali, Cornelia & Beerhues, Ludger (2012). "Phytoalexins of the Pyrinae: Biphenyls and dibenzofurans". Beilstein J. Org. Chem. 8: 613–620. doi:10.3762/bjoc.8.68.