Biological catalysts, characteristics

Enzymes are biological catalysts. Without their presence in a cell, most biochemical reactions would not proceed at the required rate. The physicochemical and biological properties of enzymes have been investigated since the early 1800s. The unrelenting interest in enzymes is due to several factors— their dynamic and essential role in the cell, their extraordinary catalytic power, and their selectivity. Two of these dynamic characteristics will be evaluated in this experiment, namely a kinetic description of enzyme activity and molecular selectivity. 

The role of the chiral coordinated ligand is to provide a pocket into which the substrate can enter in only one spatial orientation (see also Real Life 9-3 and Section 12-2). In this respect, it bears the characteristics of many enzymes, biological catalysts that function in essentially the same way (see Real Life 5-5 and Chapter 26). In the absence of the chiral ligand, a racemic mixture forms. 

Enzymes are important catalysts in biological organisms and are of increasing use in detergents and sensors. It is of interest to understand not only their adsorption characteristics but also their catalytic activity on the surface. The interplay between adsorption and deactivation has been clearly illustrated [119] as has the ability of a protein to cleave a surface-bound substrate [120]. 

Enzymes are proteins catalyzing all in vivo biological reactions. Enzymatic catalysis can also be utilized for in vitro reactions of not only natural substrates but some unnatural ones. Typical characteristics of enzyme catalysis are high catalytic activity, large rate acceleration of reactions under mild reaction conditions, high selectivities of substrates and reaction modes, and no formation of byproducts, in comparison with those of chemical catalysts. In the field of organic synthetic chemistry, enzymes have been powerful catalysts for stereo- and regioselective reactions to produce useful intermediates and end-products such as medicines and liquid crystals. ... 

Electron probe and X-ray fluorescence methods of analysis are used for rather different but complementary purposes. The ability to provide an elemental spot analysis is the important characteristic of electron probe methods, which thus find use in analytical problems where the composition of the specimen changes over short distances. The examination of the distribution of heavy metals within the cellular structure of biological specimens, the distribution of metal crystallites on the surface of heterogeneous catalysts, or the differences in composition in the region of surface irregularities and faults in alloys, are all important examples of this application. Figure 8.45 illustrates the analysis of parts of a biological cell just 1 pm apart. Combination of electron probe analysis with electron microscopy enables visual examination to be used to identify the areas of interest prior to the analytical measurement. 

There is some hope, since certain sediments are thought to be produced only by biological activities. Obviously many of the involved reactions, if not mediated by biocatalysts would require the addition of too much time and heat. In these cases it is plausible to conclude that bacteria had provided the necessary catalysts. Especially, if a specific inorganic formation is found to be associated with organic chemofossils and microfossils, it is very likely a result of biological activities. This is exemplified by stromatolltic formations. When such deposits are found, one can deduce the nature of the biological activities from the characteristics of the mineral formation. 

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