Metabolism potential energy

This potential, or protonmotive force as it is also called, in turn drives a number of energy-requiring functions which include the synthesis of ATP, the coupling of oxidative processes to phosphorylation, a metabohc sequence called oxidative phosphorylation and the transport and concentration in the cell of metabolites such as sugars and amino acids. This, in a few simple words, is the basis of the chemiosmotic theory linking metabolism to energy-requiring processes. 

The principal controls on the microbial reaction rate in our example, then, are biomass and thermodynamic drive (Fig. 33.2). Initially, in the presence of abundant lactate and arsenate, the rate is controlled by the size of the microbial population available to catalyze lactate oxidation. As the population increases, so does reaction rate. Later, as reactants are consumed and products accumulate, the reaction approaches the point at which the energy liberated by its progress is balanced by that needed in the cell to synthesize ATR Reaction rate is governed now by the energy available to drive forward the cellular metabolism, this energy represented by the thermodynamic potential factor Ft over the course of the experiment, the kinetic factors Fd and Fa play minor roles. 

Quantum mechanical approaches have been successfully used to predict hydrogen abstraction potentials and likely sites of metabolism of drug molecules [78-81]. AMI, Fukui functions, and density functional theory calculations could identify potential sites of metabolism. Activation energies for hydrogen abstraction were calculated by Olsen et al. [81] to be below 80 kj/mol, suggesting most CH groups can be metabolized which particular one depends on steric accessibility and intrinsic reactivities. 

Electrostatic isopotential (EIP) minima186 often identify sites and ease of metabolism by epoxide hydrase, an enzyme responsible for the conversion of epoxides to diols by the addition of water. Molecular electrostatic potential energy calculations also are probably the best means of identifying positions of epoxidation and, possibly, metabolism in general. In the case of aflatoxin B for example, EIP maxima and minima calculated by the CNDO/2 method all lie close to the known sites of metabolism and, in particular, the formation of the carcinogenic 2,3-epoxide is readily predicted.189... 

Herbicides could be absorbed rapidly by cultivated plants, and their effect on metabolism could be noticed a few days after application. Phytotoxic effects of different herbicides have diverse impacts on the energetic properties of plants. For instance, nicosulfuron increases energy consumption and foramsulfuron induces "metabolic burst" [100]. Phytotoxicity correlates with enthalpy increase (AH), indicating endothermic reactions [101]. This means that a great deal of the potential energy of the plant was metabolically consumed [102]. Weeds as competitors also disturb the energy efficiency in cultivated plants. 

The chemical energy in a fuel or food comes from potential energy stored in atoms due to their arrangements in the molecules. This stored chemical energy can be released when compounds undergo chemical changes, such as those that occur in combustion and metabolism. Reactions that release energy in the form of heat are called exothermic reactions. 

The useful thing about this merry-go-round as far as the cell is concerned is that it provides that critical feature of all desirable energy-releasing systems - a way for the acetic acid molecule to be carefully picked to pieces so as to release its potential energy in small steps. The cycld, as we shall find, is of great importance not only as the final stage of glucose oxidation, but in the metabolism of many other substances as well. We shall later see how, in the breakdown of both fatty and amino acids, products are formed which can enter the cycle at one of several points, to be whirled round the merry-go-round and thus oxidized. 

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