Biological processes, reaction rates

The number calculated in (b) for the concentration of H+ in blood, 4.0 X 10-8 Af, is very small. You may wonder what difference it makes whether [H+] is 4.0 X 10-8M,4.0 X 10-7Af, or some other such tiny quantity. In practice, it makes a great deal of difference because a large number of biological processes involve H+ as a reactant, so the rates of these processes depend on its concentration. If [H+] increases from 4.0 X 10-8M to 4.0 X 10-7M, the rate of a first-order reaction involving H+ increases by a factor of 10. Indeed, if [H+] in blood increases by a much smaller amount, from 4.0 X 10-8 Af to 5.0 X 10-8 M (pH 7.40----- 7.30),... 

This chapter begins by explaining how the rates of reactions are determined experimentally and showing how their dependence on concentration can be summarized by succinct expressions known as rate laws. We then see how this information gives us insight into how reactions take place at a molecular level. Finally, we see how substances called catalysts accelerate reactions and control biological processes. 

The Qxo, or temperature coefficient, is the factor by which the rate of a biologic process increases for a 10 °C increase in temperature. For the temperatures over which enzymes are stable, the rates of most biologic processes typically double for a 10 °C rise in temperature (Qjo = 2). Changes in the rates of enzyme-catalyzed reactions that accompany a rise or fall in body temperature constitute a prominent survival feature for cold-blooded life forms such as lizards or fish, whose body temperatures are dictated by the external environment. However, for mammals and other homeothermic organisms, changes in enzyme reaction rates with temperature assume physiologic importance only in circumstances such as fever or hypothermia. 

Bioprocesses for the removal of nitrogen oxides from polluted air are an interesting alternative [58], but current reaction rates are still too low for large-scale applications. Advanced biological processes for the removal of NO from flue gases are based on the catalytic activity of either eukaryotes or prokaryotes, e.g. nitrification, denitrification, the use of microalgae and a combined physicochemical and biological process (BioDeNO ). 

The studies of structure and reactivity of organosilver radicals are significant to understand the mechanism of catalytic and biological processes. However, the radical reactions are very fast and in solution can be studied only by time-resolved techniques. Zeolites are well-suited for radical investigations because the reaction rates are much slower due to the sterical hindrances of the silicaalumina lattice. 

The enzymatic activity in soil is mainly of microbial origin, being derived from intracellular, cell-associated or free enzymes. Only enzymatic activity of ecto-enzymes and free enzymes is used for determination of the diversity of enzyme patterns in soil extracts. Enzymes are the direct mediators for biological catabolism of soil organic and mineral components. Thus, these catalysts provide a meaningful assessment of reaction rates for important soil processes. Enzyme activities can be measured as in situ substrate transformation rates or as potential rates if the focus is more qualitative. Enzyme activities are usually determined by a dye reaction followed by a spectrophotometric measurement. 

The study of reaction rates or kinetics of a particular denaturation process of a protein therapeutic can provide valuable information about the mechanism, i.e., the sequence of steps that occur in the transformation of the protein to chemically or conformationally denatured products. The kinetics tell something about the manner in which the rate is influenced by such factors as concentration, temperature, excipients, and the nature of the solvent as it pertains to properties of protein stability. The principal application of this information in the biopharmaceutical setting is to predict how long a given biologic will remain adequately stable. 

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