Terpenes
Metabolism is the sum of all the chemical reactions that occur inside the organism. The products of photosynthesis, cellular respiration, protein synthesis, lipid synthesis and many others are all beneficial in the existence and survival of the organism. The molecules produced in these processes are essential in the maintenance of structural and functional integrity of the cell. Primary metabolites are molecules that are commonly found inside the cell like amino acids, lipids, proteins, and nucleic acids. These are also known as the basic molecular machinery of the cell. However, during the synthesis various materials inside the cell there are also other molecules produced other than the basic molecules found inside the cell these are known as secondary metabolites or secondary products. One of these products are groups of molecules known as terpenoids, which are functionally and chemically diverse group of molecules.
Terpenes are examples of terpenoids, which are known as complex lipophilic substances derived from a simple five-carbon unit. The family of terpenes includes hormones gibberelins and abscisic acid; the carotenoid pigments carotene and xanthophyll; sterols like ergosterol, sitosterol, and cholesterol; and sterol derivatives like cardiac glycosides; latex, which is the basis for natural rubber; and many essential oils present in plants which are responsible for their distinctive odors and flavors. Cytokinin and chlorophyll are not terpenes but do contain terpenoid side chains. The biosynthetic pathway for terpenes and terpene derivatives is called mevalonic acid pathway. Terpenoids are also known as isoprenoid compounds which are highly volatile and contributes to air pollution. There are members of the groups which are considered primary metabolites however, majority are secondary metabolites where many of serve as toxins or feeding deterrents to herbivorous insects. All members of terpenoids play significant role in plant growth and development. Other members of terpenoids include steroids and sterols with 30 carbon atoms, polyterpenes with 40 carbon atoms.
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Phenolic compounds
Phenolics or polyphenols are large and diverse group of compounds ranging from simple phenolics to very large and complex polymers like tannins and lignin including flavonoid pigments. One of their functions in their involvement in plant-herbivore interactions. The biosynthesis of phenolics follows the shikimic acid pathway where it begins in the synthesis of amino acids phenylalanine, tyrosine and tryptophan. These are further synthesized from phosphoenolpyruvate and erythrose-4-phosphate. For simple phenolics synthesis starts with the deamination of phenylalanine to cinnamic acid, which is made possible by the action of the enzyme phenylalanine ammonia lyase (PAL). The following are examples of phenolics: Coumarins are lactones which gives new-mown hay its characteristic sweet odor. It is also a constituent of Bergamot oil used to flavor pipe tobacco, tea and other products. Lignin is a highly complex and branched polymer of three simple phenolic alcohols. The alcohols are oxidized to free radicals by the ubiquitous plant enzyme peroxidase. These free radicals then react spontaneously and randomly to form lignin. These are basically found in plant cell walls especially in the xylem.
Its primary function is for mechanical strength and rigidity of woody stems. They are highly insoluble and is second in abundance next to cellulose. Flavonoids are large group pf compounds responsible for brilliant color s of flowers, fruits, bracts and sometimes leaves from various shades of scarlet, pink, purple and blue. This colorization is made by antocyanins which belong to flavonoids. They are phenylpropane derivatives and are popularly used as dyes. Three major groups include flavones, flavonols, and anthocyanidins. Tannins are used to convert hides to leather. These contain phenol derivatives that bind to, and thus denature proteins. Tannins also deter feeding by many animals. It also suppress growth rate and survivorship. They are somewhat classified as toxic to animals. Another important examples of secondary metabolites are alkaloids. Alkaloids are also very large group of secondary metabolites whose function depends on their pharmacological properties and medical applications. The principal characteristics include solubility in water, with at least one nitrogen atom, and high biological activity. They are commonly synthesized from various amino acids like tyrosine, tryptophan, ornithine, argenine and lysine. Examples of these include morphine, codeine, paraverine, berberine, lupinine, senecionine, lycotonine, scopolamine, atropine, vinblastine, vincristine, cocaine, nicotine and caffeine. Generally, they have bitter taste and are considered toxic hence, utmost care must be observed in dealing with many members of this group.
Nitrogen–containing compounds
Along with many organic compounds known, nitrogen compounds play very significant role in growth and development of the organism, not forget to mention its role in industrial production of fertilizers essential to plant life and food production. Considering the strong bond that holds N2 gas it is accompanied by greater amount of energy and considered one of the strongest bonds known. In connection to this, the greater energy holds by this element also requires a tantamount energy to break it. Recall that N2 is not directly consumed by plants, it has to be broken down and converted into more soluble form acceptable to the physico-chemical properties of plants. Its addition to organic framework resulted in the production of two families of compounds. These are amines and amides. Amines are derivatives of ammonia and contain carbon-nitrogen bonds. Water solubility of this group is shown in the length of carbon chains where smaller amines are soluble while larger members of the group have lesser solubility. It can be observed that amines have pungent or noxious odors this is evident in ammonia.
This is associated in the breakdown of proteins in animal cells resulting to the production of unpleasant odors. They are economically important in the field of medicine and in industry where dyes are produced. Amides have nitrogen atoms which are attached to carbonyl carbon atoms. Simple amides are derivatives of carboxylic acids. They can also be produced when carboxylic acids react with amines or ammonia. This has a biological importance in the formation of proteins. Among the important polyamides are nylons, these materials are known for their strength and rigidity. There are a variety of drugs from amides like paracetamol, penicillin and LSD. There are also other nitrogen containing compounds like azides, nitrogen oxides and others used as explosives or prepellants. Hence, nitrogen compounds are indeed essential in the survival of organisms.
Chlorophylls and Haems
Chlorophylls also known as the blood of plants because of their similarity in pH. They are known as the most significant pigments in plants because of their highly significant and incomparable role in photosynthesis. Indeed, we owe a lot to these pigments for it is for their ability to capture light that makes it possible to produce the food that we eat. They are known to be vital entities in the biological systems. There are three kinds of chlorophyll, chlorophyll a which is responsible for photosynthesis commonly found in plants, algae and cyanobacteria; chlorophyll b common to green algae and plants; and chlorophyll c found in members of Chromista and dinoflagellates. The first phase of chlorophyll biosynthesis starts in the conversion of glutamic acid to 5-aminolevulinic acid (ALA). Later on two molecules of ALA will form porhobilinogen (PBG) to form pyrrole rings in chlorophyll. The four molecules of PBG will form the porphyrin structure.
The final product of this process if protoporphyrin IX. Depending on the type of metal (magnesium or iron) to be inserted into the center of the porphyrin will dictate whether chlorophyll or heme will be formed. If magnesium, chlorophyll will be formed, and if it is an iron, heme will be produced. The succeeding phase in chlorophyll biosynthesis includes the formation of fifth ring (ring E) to form protochlorophyllide, this is made possible by the enzyme protochlorophyllide oxidoreductase (POR). Heme plays significant roles in various molecular processes. They are the most important porphyrin containing compound. It is a ferroprotoporphyrin exhibited by the presence of iron atom. The pyrrole rings are known as I, II, III, IV with bridges as alpha, beta, gamma and delta. Type III is most common in the biological systems. Heme biosynthesis starts in ALA synthesis made possible by ALA synthase. Next, is the formation of PBG. The third step is the formation of uroporphyrinogen (UPG). This is done by enzymes PBG-deaminase (Uroporhyrinogen I-synthase) and Iroporphyrinogen-III-cosynthase. The fourth step is the synthesis of coproporphyrinogen (CPG-III). The fifth step is the synthesis of protoporphyrinogen (PPG-III). The sixth step is the generation of protoporphyrin-9 (PP) by the action of protoporphyrin-III (PP-III). The seventh and the final step is the generation of heme by the participation of enzymes heme synthase or ferrochelatase. Heme is associated in hemoglobin known as the iron—containing substance in the blood. It is also in heme group where higher affinity of oxygen can be observed as well as nitric oxide and carbon monoxide.
It is actually in the heme group where atoms of oxygen bind during transport and circulation. Other functions of heme revolve in respiration, sensing of diatomic gases, drug detoxification, signal transduction and regulation of transcription, translation, various activities in protein synthesis, and differentiation. The significant role of heme lies in many cellular functions and in metabolism.
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