Answer to Question #101231 in Chemistry for Abhishek

Question

a) How is the standard free energy for chemical reactions different from the standard free energy for biochemical reactions? With the help of an example explain the significance of coupling in biological reactions.


b) Standard free energy change alone cannot predict the direction of a biochemical reaction. Comment.

Answer 1

a)In a cell, there are many reactions, especially in biosynthesis processes, a change in free energy is greater than zero, so that this reaction passes, it is necessary to communicate energy to the system, which in chemical reactions most often occurs due to heating of the system, in biological systems this is impossible because of primarily protein denaturation. Therefore, a biological workaround has appeared in biological systems: a system of conjugated reactions. The standard free energy in a biochemical reaction is not released immediately, but in small portions in a complex series of chemical transformations (conjugated). In living organisms, the energy released during glucose oxidation is not immediately consumed in various life processes, but is stored for future use in various energy-rich compounds, such as phosphoric acid esters (ATP, LDF, creatine and arginine phosphates, etc.).

b)Biochemical processes in the body occur spontaneously in a certain direction, ensuring their normal functioning. Changes in the enthalpy or internal energy of the system occurring in accordance with the first law of thermodynamics allow us to quantitatively determine the thermal effect of the reaction, the conversion of various forms of energy, the exchange parameters of biochemical systems of matter and energy with the environment, but these thermodynamic functions cannot serve as criteria determining the direction of reactions, the possibility of their spontaneous implementation. They also do not allow us to estimate how much energy a biochemical system must receive in order to initiate spontaneous transformation in it. It should also be noted that, in bioenergy systems, the change in free energy, as a rule, is not equal to zero, which is observed upon the occurrence of thermodynamic equilibrium. Therefore, biochemical systems in the course of transformations of substances almost never reach true chemical equilibrium. They are characterized by the so-called stationary states, when certain rates of the influx of substances and energy into the system and their outflow from the system are maintained, since the products formed during the reaction do not accumulate, but undergo further transformations. When a stationary state is reached, maximum rates of biochemical transformations are provided, which are also accompanied by a significant decrease or increase in free energy.