Metabolic process enthalpies

Suppose we know the reaction enthalpy for one temperature but require it for another temperature. For instance, the temperature of the human body is about 37°C, but the data in Appendix 2A are for 25°C. Does an increase of 12°C make much difference to the reaction enthalpy of a metabolic process ... 

This forms the basis of constructing an enthalpy budget in which the total enthalpy flux is compared with the scalar heat flux, 7q(W m-3), obtained from dividing heat flow by size (volume or mass) of the living matter. If account is made of all the reactions and side reactions in metabolism, the ratio of heat flux to enthalpy flux, the so-called energy recovery ( Yq/H = Jq/Jh) will equal 1. If it is more than 1, then the chemical analysis has failed fully to account for heat flux and if it is less than 1, then there are undetected endothermic reactions. Account for all reactions may seem a formidable task, but it should be borne in mind that anabolic processes dissipate insignificant amounts of heat compared with those of catabolism and that ATP production and utilization are balanced in cells at steady-state. Catabolism is generally limited to a relatively few well-known pathways with established overall molar enthalpies. So, as will be seen later, the task is by no means mission impossible. ... 

Entropy is closely related to heat (enthalpy) and energy. If all the ATP available from catabolic processes were used for anabolism (chemical synthesis), up to ten times more cellular material could be produced. First investigations of this large outflow of entropy from growing cells have been made by Bormann [40] however, classical thermodynamics are hardly applicable to complex, nonequilibrium metabolic systems and must be extended [458]. 

Cells metabolize in an aqueous environment and, except for those of the cells, the thermodynamic properties of the reactants and products of growth-processes are those of these substances in aqueous solution. Values for the free energy, enthalpy, and entropy of formation of all substances from the elements at 298.15 K and 1 atm are referred to as thermodynamic properties. These can be found in several compendia [32-34] listed for quantities of one mol in a given standard state. In aqueous solution, all substances are taken to be at a concentration of one mol at unit activity for values of A , and of a hypothetical one mol at infinite dilution for Af//°. Values for Af5" can be calculated using the following form of the Gibbs free energy equation, where the superscript refers to the aqueous standard state. 

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