Bulk biological elements

Bulk biological elements Trace elements believed to be essential [ J Possibly essential trace elements... 

Bulk biological I I Trace elements believed ] Possibly essential... 

I I ttie main constituents of biological molecules n bulk biological inorganic elements I esse nti a I trace ino rga n ic e I e m ents I I trace inorganic elements, essential for some species... 

It can be concluded that, in the field of RM certification, NAA represents a major analytical technique contributing significantly to the certification of element contents in environmental and biological RMs, as was also pointed out earlier (Dyb-czynski 1980 1995), and also provides the bulk of the hterature data on NIST SRMs (Gladney et al. 1987,1993). NAA also has a similar position in the field of geological RMs (Roelandts 1991). It possesses unique quality assurance and self-verification aspects (Becker 1993 Byrne 1993 Byrne and Kucera 1997), though these in-built features are rarely exploited in fuU at present. It should be reahzed that the advanta-... 

FIG. 2.1. The Periodic Table of the elements, the full understanding of which provides ideally a reductionist approach to the explanation of chemistry. The essential bulk and trace elements for living cells are also shown but knowledge of them is not in any way adequate for an explanation of biology... 

Chemical elements essential to life forms can be broken down into four major categories (1) bulk elements (H, C, N, O, P, S) (2) macrominerals and ions (Na, K, Mg, Ca, Cl, PO4A SC>4 ) (3) trace elements (Fe, Zn, Cu) and (4) ultratrace elements, comprised of nonmetals (F, I, Se, Si, As, B) and metals (Mn, Mo, Co, Cr, V, Ni, Cd, Sn, Pb, Li). The identities of essential elements are based on historical work and that done by Klaus Schwarz in the 1970s.1 Other essential elements may be present in various biological species. Essentiality has been defined by certain... 

Biomineralization. In biomineralization, inorganic elements are extracted from the environment and selectively precipitated by organisms. Usually, templates consisting of suitable macro-molecules serve as a substrate for the heterogeneous nu-cleation of bulk mineralized structures such as bone, teeth and shells. Biological control mechanisms are reflected not only in the type of the mineral phase formed but also in its morphology and crystallographic orientation (Mann et al., 1989 Lowenstamm and Weiner, 1989). Two examples (perhaps oversimplified) may illustrate the principle (Ochial, 1991) ... 

Of the various factors that cause redox disequilibria, the most effective are biologic activity (photosynthesis) and the metastable persistence of covalent complexes of light elements (C, H, O, N, S), whose bonds are particularly stable and difficult to break (Wolery, 1983). For the sake of completeness, we can also note that the apparent redox disequilibrium is sometimes actually attributable to analytical error or uncertainty (i.e., difficult determination of partial molalities of species, often extremely diluted) or even to error in speciation calculations (when using, for instance, the redox couple Fe /Fe, one must account for the fact that both Fe and Fe are partly bonded to anionic ligands so that their free ion partial molalities do not coincide with the bulk molality of the species). 

In almost all instances of biological mineralization fibrous proteins represent the bulk of the organic matrix. In the past, this phenomenon has been interpreted to mean that proteins such as collagen, keratin or elastin are the key elements in mineralization by providing nucleation sites and at the same time offering structure and space for oriented crystal growth. However, with the advance in the field of biomineralization this model came under severe attack. At present, there is no universal concept which could explain all the intriguing facets of phosphate deposition in cellular systems. 

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