Thermodynamics in living systems

Strategy From the information given we see that neither the reactant nor the product is at its standard state of 1 atm. To determine the direction of the net reaction, we need to calculate the free-energy change under nonstandard-state conditions (AG) using Equation (18.13) and the given AG° value. Note that the partial pressures are expressed as dimensionless quantities in the reaction quotient Qp because they are divided by the standard-state value of 1 atm (see p. 621 and Table 18.2). 

Because AG 0, the net reaction proceeds from left to right to reach equUihrium. 

Check Note that although AG° 0, the reaction can be made to favor product formation initially by having a small concentration (pressure) of the product compared to that of the reactant. Confirm the prediction by showing that Qp Kp. 

Many biochemical reactions have a positive AG° value, yet they are essential to the maintenance of life. In living systans these reactions are coupled to an energetically favorable process, one that has a negative AG° value. The principle of coupled reactions is based on a simple concept We can use a thermodynamically favorable reaction to drive an unfavorable one. Consider an industrial process. Suppose we wish to extract zinc from the ore sphalerite (ZnS). The following reaction will not work because it has a large positive AG value  

A mechanical analog for coipled reactions. We can make the smaller weight move upward (a nonspontaneous process) by couping it with the faling of a larger wei.  

Many biochemical reactions have a positive AG° value, yet they are essential to the maintenance of life. In living systems, these reactions are coupled to an energetically favorable process, one 

On the other hand, the combustion of sulfur to form sulfur dioxide is favored because of its large negative AG° value  

By coupling the two processes, we can bring about the separation of zinc from zinc sulfide. In practice, this means heating ZnS in air so that the tendency of S to form SO2 will promote the decomposition of ZnS  

Coupled reactions play a crucial role in our survival. In biological systems, enzymes facilitate a wide variety of nonspontaneous reactions. In the human body, for example, food molecules, represented by glucose (C6H12O6). are converted to carbon dioxide and water during metabolism, resulting in a substantial release of free energy  

The function of ATP is to store free energy until it is needed by cells. Under app-opriate conditions, ATP undergoes hydrolysis to give ADP and phosphoric add, with a release of 31 kJ/mol of free energy, which can be used to drive energetically unfavorable reactions, such as protdn synthesis. 

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Bioenergetics of Self-Assembly Energetics of Protein Folding Ligand-Operated Membrane Channels Protein-Protein Interactions Thermodynamics in Living Systems... 

Thermodynamics in Living Systems Many reactions of biological importance are nonspontaneous. By coupling such reactions to those that have a negative Gibbs free energy change with the aid of enzymes, the net reaction can be made to proceed to yield the desired products. 

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