Types And Forms Of Metabolism In Plants Pdf
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The vast and versatile pharmacological effects of medicinal plants are basically dependent on their phytochemical constituents. Generally, the phytochemical constituents of plants fall into two categories based on their role in basic metabolic processes, namely primary and secondary metabolites.
Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen atoms.
Metabolism pronounced: meh-TAB-uh-liz-um is the chemical reactions in the body's cells that change food into energy. Our bodies need this energy to do everything from moving to thinking to growing. Specific proteins in the body control the chemical reactions of metabolism. Thousands of metabolic reactions happen at the same time — all regulated by the body — to keep our cells healthy and working. After we eat food, the digestive system uses enzymes to:.
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The vast and versatile pharmacological effects of medicinal plants are basically dependent on their phytochemical constituents. Generally, the phytochemical constituents of plants fall into two categories based on their role in basic metabolic processes, namely primary and secondary metabolites. Primary plant metabolites are involved in basic life functions; therefore, they are more or less similar in all living cells.
On the other hand, secondary plant metabolites are products of subsidiary pathways as the shikimic acid pathway. In the course of studying, the medicinal effect of herbals is oriented towards the secondary plant metabolites. Secondary plant metabolites played an important role in alleviating several aliments in the traditional medicine and folk uses. In modern medicine, they provided lead compounds for the production of medications for treating various diseases from migraine up to cancer. Secondary plant metabolites are classified according to their chemical structures into various classes.
In this chapter, we will be presenting various classes of secondary plant metabolites, their distribution in different plant families and their important medicinal uses. Herbal Medicine.
Plant chemistry is the basis of the therapeutic uses of herbs. A good knowledge of the chemical composition of plants leads to a better understanding of its possible medicinal value. Modern chemistry has described the role of primary plant metabolites in basic life functions such as cell division and growth, respiration, storage and reproduction.
They include the components of processes such as glycolysis, the Krebs or citric acid cycle, photosynthesis and associated pathways. Primary metabolites include small molecules such as sugars, amino acids, tricarboxylic acids, or Krebs cycle intermediates, proteins, nucleic acids and polysaccharides.
Eventually, the primary metabolites are similar in all living cells [ 1 ]. Secondary plant metabolites are numerous chemical compounds produced by the plant cell through metabolic pathways derived from the primary metabolic pathways. The concept of secondary metabolite was first defined by Albrecht Kossel, Nobel Prize winner for physiology or medicine in [ 2 ]. Thirty years later, Czapek described them as end-products [ 3 ]. In the middle of the twentieth century, advances of analytical techniques such as chromatography allowed the recovery of more and more of these molecules, and this was the basis for the establishment of the discipline of phytochemistry.
Secondary metabolites have shown to possess various biological effects, which provide the scientific base for the use of herbs in the traditional medicine in many ancient communities. They have been described as antibiotic, antifungal and antiviral and therefore are able to protect plants from pathogens.
Besides, they constitute important UV absorbing compounds, thus preventing serious leaf damage from the light. It was noticed that some herbs as forage grasses such as clover or alfalfa can express estrogenic properties and interact with fertility of animals [ 4 ]. Secondary plant metabolites are classified according to their chemical structures into several classes. In this chapter, the nature of secondary plant metabolites will be discussed as a foundation for a review of the main categories of constituents considered to be of therapeutic importance.
Each section includes an overview of a class of the secondary plant metabolites regarding structure, botanical distribution and generalizations about pharmacology, followed by examples of representative molecules. The classes of secondary plant metabolites include: Phenolics.
Phenolics probably constitute the largest group of plant secondary metabolites. They are widespread in plants where they contribute significantly to the color, taste and flavor of many herbs, foods and drinks. Some phenolics are valued pharmacologically for their anti-inflammatory activities such as quercetin or antihepatotoxic properties such as silybin.
Others exert phytoestrogenic activity as genistein and daidzein, while others are insecticidal as naringenin [ 5 ]. Many of the phenolic molecules are also effective antioxidants and free radical scavengers, especially flavonoids. Phenolics can be classified according to their structure or biosynthetic origin. According to their structures, phenolics can be classified into: Simple phenolics. It also inhibits insulin degradation and promotes smooth muscle relaxation [ 6 ].
The phenolic compounds in this group vary according to their functional group, which may be hydroxyl, aldehydic, or carboxylic group; these include eugenol a phenolic phenylpropane , vanillin a phenolic aldehyde and salicylic, ferulic and caffeic acids phenolic acids.
Hydroquinone is also among the most widely distributed of the simple phenols, occurring in a number of plants as the glycoside arbutin. Glycoside formation is common, and the widely distributed glycoside coniferin and other derivatives of phenolic cinnamic alcohols are precursors of lignin [ 7 , 8 ]. The pharmacological properties of these widely found constituents are probably best demonstrated by the urinary tract antimicrobial arbutin [ 9 ] and the anti-inflammatory salicylates [ 10 ].
A property shared by all phenols is antimicrobial activity. In fact, phenol itself was the first antiseptic used in surgery [ 11 ]. The pharmacological activities of many plants are attributed to simple phenolics among which the antimicrobial and diuretic activities of Arctostaphylos uva-ursi were attributed to its phenolic content [ 12 ]. Capsicum spp. Moreover, the cholagogue activity of Cynara scolymus , the anthelmintic activity of Dryopteris filix-mas , the anti-inflammatory analgesic activity of Filipendula ulmaria as well as the anticatarrhal and diuretic activities of Solidago virgaurea are all attributed to the action of simple phenolics [ 8 ].
Tannins are polyphenols which have the ability to precipitate protein. These compounds have been used for decades to convert raw animal hides into leather. In this process, tannin molecules crosslink the protein and make it more resistant to bacterial and fungal attack.
Today, however, many substances considered to be tannins by virtue of their structure and biosynthetic origin have limited, if any, ability to make leather [ 14 ]. There are two major types of tannins: hydrolyzable tannins and condensed tannins. Hydrolyzable tannins are formed from several molecules of phenolic acids such as gallic and hexahydroxydiphenic acids, which are united by ester linkages to a central glucose molecule.
Two principal types of hydrolysable tannins are gallotannins and ellagitannins, which are, respectively, composed of gallic acid and ellagic acid units. Ellagitannins found in plants of medicinal interest and for which structures have been elucidated include geraniin isolated from Geranium robertianum Herb Robert and Geranium maculatum American cranesbill [ 15 ] and tellimagrandins 1 and 2 [ 16 ] isolated from Quercus alba Oak bark , Punica granatum pomegranate and Filipendula ulmaria Meadowsweet [ 7 ].
Condensed tannins, or proanthocyanidins, are compounds whose structures are based on oligomeric flavonoid precursors and vary in the type of linkages between flavonoid units; hydroxylation patterns; stereochemistry of carbons 2, 3 and 4 of the pyran ring and the presence of additional substituents. Some drugs e. Tannin-containing drugs act as antidiarrhoeals and have been employed as antidotes in poisoning by heavy metals and alkaloids.
Epigallocatechingallate, the active principal in tea, has been shown to be antiangiogenic in mice. Vaccinium oxycoccos cranberry juice has long been used as urinary antiseptic [ 18 ], which was scientifically proven in a randomized, double-blind, placebo-controlled trial that has been carried out on elderly women [ 19 ].
Some natural coumarins have been isolated. Coumarin itself has been found in about species belonging to over 30 different families.
The richest sources of coumarin are sweet clover or melilot Melilotus spp. Aesculetin, umbelliferone and scopoletin are common coumarins present in plants both in the free state and as glycosides. Plants rich in coumarins include Atropa belladonna , Datura stramonium Solanaceae , Daphne mezereum Thymeliaceae , Ruta graveolens Umbelliferae and certain Aesculus hippocastanum Horse-chestnut Hippocastanaceae and certain Rosaceae [ 7 ]. Flavonoids are the largest group of naturally occurring phenols.
More than of these compounds are now known, with nearly occurring in the free state [ 7 ]. The structural skeleton of flavonoids includes a chroman ring bearing an aromatic ring in position 2, 3 or 4. Flavonoids may be divided into various classes according to the oxidation level of the central ring ring C. The most common of these are anthocyanins, flavones and flavonols. The flavones and their close relations are often yellow Latin flavus , yellow.
They are widely distributed in nature but are more common in the higher plants and in young tissues, where they occur in the cell sap. Recent researches have demonstrated the medicinal action of drugs containing flavonoids such as Glycyrrhiza glabra liquorice root , Chamaemelum nobile Roman chamomile and Ginkgo biloba gingko.
A number of flavonoid-containing herbs have now been included in the British Pharmacopeia, examples are Betula pendula Birch Leaf , Calendula officinalis Flower, Sambucus nigra ElderFlower , Equisetum ramosissimum Horsetail , Tilia cordata Lime Flower , Leonurus cardiaca Motherwort and Passiflora edulis passion flower.
The group is known for its anti-inflammatory and antiallergic effects, for antithrombotic and vasoprotective properties, for inhibition of tumor promotion and as a protective for the gastric mucosa [ 21 , 22 ]. More complex are the furanochromones, the active constituents of the fruits of Ammi visnaga. Xanthones are found mainly in the Gentianaceae and Guttiferae, otherwise scattered sporadically throughout the plant kingdom as in the Moraceae and Polygalaceae. Polygala nyikensis is used by the highlanders of Malawi and bordering countries to treat various skin problems of fungal origin.
The root of the plant was recently shown to exert its antifungal activity owing to the presence of xanthones [ 23 ]. Stilbenes are a relatively small, but widely distributed, group of plant secondary metabolites found mostly as heartwood constituents in a heterogeneous assembly of plant species.
They are especially important in the heartwood of trees of the genera Pinus Pinaceae , Eucalyptus Myrtaceae and Madura Moraceae [ 1 ]. The para-hydroxylated compound, resveratrol, is the most widespread stilbene in nature.
Resveratrol possesses estrogen-like activity and occurs in Picea , Pinus , the Fabaceae, Myrtaceae and the Vitaceae [ 24 ]. Lignans are dimeric compounds formed essentially by the union of two molecules of a phenylpropene derivative reported from the members of Asteraceae e.
Four major subtypes occur: dibenzylbutane derivatives, dibenzylbutryolactones lignanolides or derivatives of butanolide , monoepoxy lignans or derivatives of tetrahydrofuran and bisepoxylignans or derivatives of 3,7-dioxabicyclo 3. Many of these compounds showed antimicrobial and antifungal activities [ 1 ], while others showed cytotoxic activities such as wikstromal, matairesinol and dibenzyl butyrolactol from Cedrus deodara [ 26 ].
Alkaloids are organic compounds with at least one nitrogen atom in a heterocyclic ring. Their definition is problematic, as they do not represent a homogeneous group of compounds from any standpoint, whether chemical, biochemical, or physiological.
Except for the fact that they are all nitrogen-containing compounds, no general definition fits all alkaloids. Alkaloids can be divided according to their basic chemical structure into different types. The following are basic types of alkaloids: acridones, aromatics, carbolines, ephedras, ergots, imidazoles, indoles, bisindoles, indolizidines, manzamines, oxindoles, quinolines, quinozolines, phenylisoquinolines, phenylethylamines, piperidines, purines, pyrrolidines, pyrrolizidines, pyrroloindoles, pyridines and simple tetrahydroisoquinolines [ 28 ].
Alkaloids are not common in lower plants. Lysergic acid derivatives and sulfur-containing alkaloids, e. Concerning the pteridophytes and gymnosperms alkaloids reported for their medicinal uses include the lycopodium, ephedra and Taxus alkaloids. Alkaloids are unevenly distributed among the angiosperms. However, there is no report for the presence of alkaloids in Salicales, Fagales, Cucurbitales and Oleales dicot orders till the present time [ 7 ].
Alkaloids demonstrate a diverse array of pharmacological actions including analgesia, local anesthesia, cardiac stimulation, respiratory stimulation and relaxation, vasoconstriction, muscle relaxation and toxicity, as well as antineoplastic, hypertensive and hypotensive properties. The activity of alkaloids against herbivores, toxicity in vertebrates, cytotoxic activity, the molecular targets of alkaloids, mutagenic or carcinogenic activity, antibacterial, antifungal, antiviral and allelopathic properties have been reported in literature.
Many alkaloids are sufficiently toxic to animals to cause death if eaten. Several e. Nicotine is found in the tobacco plant Nicotiana tabacum and other Nicotiana species; it has tranquilizing properties and is the addictive component of tobacco.
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Raja and Ramasamy Vijayakumar. Reviewed: June 26th Published: September 5th Secondary Metabolites - Sources and Applications. The metabolism can be defined as the sum of all the biochemical reactions carried out by an organism. Metabolites are the intermediates and products of metabolism and are usually restricted to small molecules. Though secondary metabolites are derived from primary metabolism, they do not make up basic molecular skeleton of the organism. Its absence does not immediately curtail the life of an organism, a feature contrary to primary metabolite, but survival of the organism is impaired to a larger extent.
in different types of plant tissue. Heterogeneity of mitochondrial form and function. The changes in metabolic activity that occur with changes in development of.
An Introductory Chapter: Secondary Metabolites
These enzyme -catalyzed reactions allow organisms to grow and reproduce, maintain their structures, and respond to their environments. The word metabolism can also refer to the sum of all chemical reactions that occur in living organisms, including digestion and the transport of substances into and between different cells, in which case the above described set of reactions within the cells is called intermediary metabolism or intermediate metabolism. In various diseases, such as type II diabetes , metabolic syndrome , and cancer , normal metabolism is disrupted. Metabolic reactions may be categorized as catabolic — the breaking down of compounds for example, the breaking down of glucose to pyruvate by cellular respiration ; or anabolic — the building up synthesis of compounds such as proteins, carbohydrates, lipids, and nucleic acids. Usually, catabolism releases energy, and anabolism consumes energy.
Alkylating agents are most active in the resting phase of the cell. There are several types of alkylating agents used in chemotherapy treatments:. The vinca alkaloids are made from the periwinkle plant catharanthus rosea.
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