Biochemical reactions temperature effects

The equations in the preceding sections are general, but now we will concentrate on the interpretation of measurements of apparent equilibrium constants at a single temperature because this is the situation for most studies of biochemical reactions. The effect of temperature will be treated in the next chapter. Since we will be considering experimental data, formation properties will be used. Equation 3.3-4 for the transformed chemical potential of a species can be written as... 

Control of relative humidity is needed to maintain the strength, pHabiUty, and moisture regain of hygroscopic materials such as textiles and paper. Humidity control may also be required in some appHcations to reduce the effect of static electricity. Temperature and/or relative humidity may also have to be controlled in order to regulate the rate of chemical or biochemical reactions, such as the drying of varnishes, the appHcation of sugar coatings, the preparation of synthetic fibers and other chemical compounds, or the fermentation of yeast. 

Generally, in an equation of a chemical reaction rate, the rate constant often does not change with temperature. There are many biochemical reactions that may be influenced by temperature and the rate constant depends on temperature as well. The effect of temperature on... 

Because cryosolvents must be used in studies of biochemical reactions in water, it is important to recall that the dielectric constant of a solution increases with decreasing temperature. Fink and Geeves describe the following steps (1) preliminary tests to identify possible cryosolvent(s) (2) determination of the effect of cosolvent on the catalytic properties (3) determination of the effect of cosolvent on the structural properties (4) determination of the effect of subzero temperature on the catalytic properties (5) determination of the effect of subzero temperature on the structural properties (6) detection of intermediates by initiating catalytic reaction at subzero temperature (7) kinetic, thermodynamic, and spectral characterization of detected intermediates (8) correlation of low-temperature findings with those under normal conditions and (9) structural studies on trapped intermediates. 

The effect of temperature on the apparent Henry s law constant at ionic strength 0.25 M is shown by Fig. 8.1. The effect of ionic strength on the Henry s law constant at 298.15 K and 0.25 M ionic strength is shown by Fig 8.2. The equilibrium constant expression for a biochemical reaction involving carbon dioxide at a specified pH can be written as... 

Enthalpies of Reaction from the Standard Enthalpies of Formation of Species II 10.3 Calculation of Standard Transformed Entropies of Biochemical Reactions I, 10.4 Effect of Temperature... 

Together with biochemical reactions catalyzed by enzymes of yeasts and bacteria, chemical reactions also occur between molecules already present in the must, those gradually extracted from the grape solids during fermentation, those derived from metabolism and, possibly, also those released by the wood. For many of them, the temperature and dissolved oxygen parameters related to technological operations of the winery can have dramatic effects and the quality of the final wine depends on the type and intensity of reactions taking place. 

R. A. Alberty, Effect of temperature on standard transformed Gibbs energies of formation of reactants at specified pH and ionic strength and apparent equilibrium constants of biochemical reactions, J. Phys. Chem. 105 B, 7865-7870 (2001). (Supplementary Information is available.)... 

Enzymes are catalytically active proteins that are involved in every in vivo transformation. They enhance the rates of biochemical reactions by 10 to 10 2 by reduction of the free energy of activation. Two distinctive properties of enzymes are their high substrate specificity and the narrow range of conditions under which they are effective. They usually catalyze one reaction of a few substrates. Activities are dependent on pH, temperature, the presence of cofactors, as well as concentrations of substrates and products. Enzymes perform specific reactions because they possess cavities in which substrates are oriented white they are transformed (Figure 1). This process involves interaction of the substrate with amino acids of the enzyme. 

FIGURE 3.10. Typical effects of temperature on reaction rates of (A) inorganic reactions, (B) explosive reactions, and (C) biochemical reactions. 

It is apparent from the above discussion that Le ChStelier s principle is the dominant concept behind most chemical reactions in the real world. It is particularly important in biochemical reactions, and external factors such as temperature can have a significant effect on biological equilibria. Catalysts (enzymes) are also key players in many biological and physiological reactions, as we shall see in Chapter 22. 

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