In living organisms

The C exchanges with C in living organisms, but exchange ceases on death. The radioactive content decays with a half-life of 5730 years. Hence the age of a once living material may be established by determining the amount of C. 

Calcium plays an important part in structure-building in living organisms, perhaps mainly because of its ability to link together phosphate-containing materials. Calcium ions in the cell play a vital part in muscle contraction. 

Porphyrins and chlorophylls are the most widespread natural pigments. They are associated with the energy-converting processes of respiration and photosynthesis in living organisms, and the synthesis of specific porphyrin derivatives is often motivated by the desire to perform similar processes in the test tube. The structurally and biosynthetically related corrins (e.g. vitamin B,j) catalyze alkylations and rearrangements of carbon skeletons via organocobalt intermediates. The biosyntheses of these chromophores are also of topical interest. 

Indicator plants generally have an offensive odor, which varies with the selenium concentration. Other vegetable matter grown on seleniferous soils may have a sufficiently high selenium content to be toxic when ingested by animals or humans. Apart from appearance in these seleniferous plants, selenium has been considered as a variable contaminant. Selenium is a necessary micronutrient in living organisms, needed by humans as well as animals (see Mineral NUTHiENTs). 

It has been estimated that >90% of the carbohydrate mass in nature is in the form of polysaccharides. In living organisms, carbohydrates play important roles. In terms of mass, the greatest amounts by far are stmctural components and food reserve materials, in that order and both in plants. However, carbohydrate molecules also serve as stmctural and energy storage substances in animals and serve a variety of other essential roles in both plants and animals. 

BLACK LIST The Blaek List was introdueed by the EC in Direetive 76/464/EEC on dangerous substanees released into water as list I. It eontains substanees seleeted mainly on the basis of their toxieity, persistenee and aeeumulation in living organisms and in sediment. 

Biocatalyst An enzyme tliat plays a fundamental role in living organisms or in industry by activating or accelerating a bioprocess. 

Pathogen A material that is capable of producing disease in living organisms. 

Very little is known about the occurrence of 1-hydroxytryptamine and/or 1-hydroxytryptophan derivatives in living organisms. Many 1-methoxyindole derivatives have been isolated as natural products (87MI629, 88BCJ285, 92H1877, 93MI22) for the simple reason that they are stable under isolating processes. 

No 1 -hydroxytryptamine or -tryptophan alkaloid that lacks a stabilizing group on the indole nucleus has been reported yet. However, isolation of37,38a, 38b, HUN-7293 (293) (96MI69), and apicidin (301) (96TL8077) offers indirect evidence for the existence of 1-hydroxytryptamines and/or 1-hydroxytryptophans in living organisms. We believe their isolation will be reported in the near future. 

All chemical reactions, whether in the laboratory or in living organisms, follow the same "rules." Reactions in living organisms often look more complex than laboratory reactions because of the size of the biomolecules and the involvement of biological catalysis called enzymes, but the principles governing all reactions are the same. 

Alkene addition reactions occur widely, both in the laboratory and in living organisms. Although we ve studied only the addition of HX thus far, many closely related reactions also take place. In this chapter, we ll see briefly how alkenes are prepared, we ll discuss many further examples of aJkene addition reactions, and we ll sec the wide variety of compounds that can be made from alkenes. 

In living organisms, aldehyde and ketone reductions are carried out by either of the coenzymes NADH (reduced nicotinamide adenine dinucleotide) or NADPH (reduced nicotinamide adenine dinucleotide phosphate). Although... 

In living organisms, a similar process occurs, although a tliioester or acyl adenosyl phosphate is the substrate rather than a carboxylic acid chloride. 

The most common example of this process in living organisms is the reaction of the amino acid methionine with adenosine triphosphate (ATP Section 5.8) to give S-adenosylmethionine. The reaction is somewhat unusual in that the biological leaving group in this SN2 process is the triphosphate ion rather than the more frequently seen rliphosphate ion (Section 11.6). 

Both in the laboratory and in living organisms, the reactions of carbonyl compounds take place by one of four general mechanisms nucleophilic addition, nucleophilic acyl substitution, alpha substitution, and carbonyl condensation. These... 

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