Notes from Sept. 9th
Notes from Sept. 9th HORT 3440
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This 4 page Class Notes was uploaded by Meghan Shah on Tuesday September 13, 2016. The Class Notes belongs to HORT 3440 at University of Georgia taught by James Affecter in Fall 2016. Since its upload, it has received 4 views. For similar materials see Herbs, Spices, and Medicinal Plants in Biology/Anthropology at University of Georgia.
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Date Created: 09/13/16
Notes from Sept 9: Secondary Metabolites Primary vs. Secondary Metabolites in Plants ○ Carbohydrates, proteins, lipids, and nucleic acids are essential to life ▪ they’re called primary metabolites because they occur in the major metabolic pathways and processes of plants (respiration, photosynthesis, cell division, etc.) ○ Plants produce many other compounds via other metabolic pathways ▪ These are called secondary metabolites. ▪ They serve diverse functions in plants and are often the source of a plant’s medicinal or culinary value ▪ Many plant toxins belong to this group too. ○ At one time it was thought that these compounds were waster productions of metabolism. ○ We now know many of them serve important ecological functions in plants, including: ▪ attracting pollinators for fruit/seed dispersal ▪ inhibiting bacterial and fungal pathogens ▪ deterring grazing animals and herbivorous insects ▪ Inhibiting the growth of competing plants Secondary metabolites can be grouped into four large classes of compounds: ○ Terpenes, Phenolics, Alkaloids, and Glycosides. ○ Terpenes ▪ Hydrocarbons – compounds containing only carbon and hydrogen ▪ Include essential oils, resins, and polyterpenes. ▪ Range greatly in size and structure ▪ Resins are used in the production of: Pharmaceuticals Rosin Turpentine Varnishes Insecticides Chewing gum Oilbased paints ▪ Polyterpenes include the elastic compounds found in many (new world) plants Also the natural rubber from the rubber tree (Hevea brasiliensis) ▪ Taxol is a terpene obtained from the Pacific Yew ▪ Carotenoid pigments – the red, yellow, and orange pigments found in plants, like tomatoes – are terpenes too. But they’re usually classified as primary metabolites ▪ In essential oils, terpenes provide the flavor and aroma of many herbs and spices, as well as the scents used in perfumes. ○ Phenolics ▪ All contain one or more aromatic benzene rings (a ring of 6 carbon atoms and 6 hydrogen atoms attached) with one or more hydroxyl (OH) groups ▪ Large and diverse category of compounds Range from small molecules to large & complex macromolecules ▪ The natural browning of cut surfaces of apples and potatoes are caused by the interaction of phenolic compounds with oxygen in the air ▪ Some phenolic compounds are essential oils, like clove oil and bergamont (used to flavor Earl Grey tea) ▪ Flavonoids Include water soluble pigments known as anthocyanins, found in red cabbage and many flower petals ▪ Tannins Utilized as stains, dyes, inks, and tanning agents for leather Believed to function in plants by discouraging herbivores Important flavor compounds in tea, red wine, and many fruits ▪ Lignin Actually a primary metabolite found in the cell walls of many plants Gives wood its hardness and strength Composed of thousands of phenolic molecules Urushiol – contact poison in poison oak and poison ivy that causes the itchy, blistering rash Tetrahydrocannabinol (THC) – a phenolic resin and the active ingredient in marijuana ○ Glycosides ▪ Compounds made up of a sugar (usually glucose) and a nonsugar molecule ▪ When these compounds are metabolized by animals, the sugar splits off and the nonsugar component becomes physiologically active. The nonsugar component is typically a terpene, steroid (a type of lipid), or phenolic compound ▪ Saponins Combination of a sugar and a steroid Forms a soapy lather when mixed with water Used in shampoos and detergents Bitter tasting; cause gastric upsets Soapwort – Saponaria officinalis Saponins from yams are the source of steroids used in the manufacture of human sex hormones 10 species of Dioscorea (yams) are important food crops in the tropics They are vines that produce large tubers that are rich in starch, some with additional protein The saponins of yams are a type of steroid that has been used to make human sex hormones and cortisone ← Early research on the development of the birth control pill was based on diosgenin extracted from yams and shown to inhibit ovulation ← Today, synthetics have largely replaced natural compound in the production of birth control pills ▪ Cardiac Glycosides The active portion of the molecule is similar to a steroid These affect the heartbeat Fatal if consumed in large doses Digitoxin from foxglove is an important medicine for congestive heart failure ▪ Cyanogenic Glycosides These release deadly hydrogen cyanide (HCN) when metabolized Cassava is the 6 most important food crop in the world, but it’s edible tubers can cause death by cyanide poisoning if they’re not processed to remove the toxins by: Soaking Boiling Fermenting Other methods ○ Alkaloids ▪ Nitrogencontaining secondary metabolites that are synthesized by/from various amino acids ▪ Known for their effects on mammalian physiology, especially the central nervous system Many are similar to neurotransmitters found in the brain Most are considered psychoactive ▪ Some are stimulants: Caffeine Cocaine Ephedrine ▪ Some are depressants: Morphine Codeine ▪ In high doses, many alkaloids are deadly poisons, such as the nicotine in tobacco ▪ Some alkaloids, such as mescaline, the tropane alkaloids, and the ergot alkaloids, are hallucinogenic The release of volatile Sulphurcontaining compounds when cells are damaged is the reason we value many plants in the mustard and onion families. ○ It explains the delayed reactions when we chew mustard seeds ○ Isothiocyanates are sulphurcontaining molecules found in the mustard fam ▪ The substrate compound, glucosinate, and the enzyme, myrosinase, are stored within different compartments of the cells When cells are broken or crushed, like when we chew them, the substrate and enzyme are brought into contact and they reaction, producing the spice flavor compound isothiocyanate ○ The pungent flavor of many plants in the onion fam are due to the presence of various volatile sulphur compounds that are released when the tissues are cut, and the substrate compound and enzyme are brought into contact ▪ Garlic is in the onion family; the active ingredient in garlic is allicin. ▪ The chemically similar active ingredient from onions is known as “the lacrimatory factor” Cutting onions under water will wash away some of the lacrimony factor Cutting onions cold will retard the enzyme activity After digestion, the sulphur compounds are transported by the blood stream into the lungs, where they diffuse into exhaled air That gives you garlic breath Summary of Major Groups of Secondary Metabolites ○ Terpenes – essential oils, resins, polyterpenes ○ Phenolics – flavonoids, tannin, lignin ○ Glycosides – saponins, cardiac glycosides, cyanogenic glycosides ○ Alkaloids – sulphurcontaining compounds, isothiocyanates (mustards), alliin/allicin (onions) Our ability to taste certain compounds is genetically determined ○ It all depends on which alleles you’re carrying in your DNA Flower//Plant Meanings for “Tussie Hussies” ○ Bachelor’s button – hope in love ○ Jasmin – availability ○ Sweet Willian – gallantry ○ Chrysanthemums – cheerfulness ○ Hyacinth – playfulness ○ Basil hatred ○ Aloe – sorrow, bitterness ○ Evening Primrose – inconstancy ○ Hop – injustice ○ Marigold – mental anguish ○ Hellebore – female inconstancy
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