Anabolic equations

Other than using the electron equivalence of the substrate and the biomass to construct anabolic equations as described in Section 2.3.6, carbon equivalence has also been used, examples of which are found in references [26, 27]. In this latter method, the carbon in the quantity of substrate used to form the biomass is equivalent to the quantity of carbon in the biomass. Whereas this can be done as a chemical representation, the problem exists that unless the substrate and the cells have exactly the same degree of reduction, 02(aq) will be either a reactant or a product of anabolism. Except to the negligible extent noted in Section 2.4.6., OjCaq) does not enter into anabolism. 

Two important implications of the reactions described in Equations (5.1) and (5.2) are (i) that redox reactions play an important role in metabolic transformations, with the cofactors nicotinamide adenine dinucleotide (NAD+) acting as electron acceptor in catabolic pathways and nicotinamide adenine dinucleotide phosphate (NADPH) as electron donor in anabolism, and (ii) that energy must be produced by catabolism and used in biosyntheses (almost always in the form of adenosine triphosphate, ATP). 

Comparing this equation with the equation for the complete oxidation of palmitoyl-CoA (see table 18.1, equation 1), we find major differences in carriers and intermediates. The principal electron carrier in the anabolic pathway is the NADPH-NADP+ system in the catabolic pathway, /3 oxidation, the principal electron carriers are FAD-FADH2 and NAD+-NADH. The second striking difference between the two pathways is that malonyl-CoA is the principal substrate in the anabolic pathway but plays no role in the catabolic pathway. These differences reflect the fact that the two pathways do not share common enzymes. Indeed, in animal cells the reactions occur in separate cell compartments biosynthesis takes place in the cytosol, whereas catabolism occurs in the mitochondria. 

This exponential decay rate for R in a stationary system will now be compared with that for a system in which X oscillates due to oscillations in a or 0. First, if the oscillations are driven solely by the anabolic term a and the rate of catabolism 0 remains time-independent, inspection of equations (6-10) shows that, for the steady state oscillation, relations (11) and (12) hold true. That is, the rate of removal of labeled compounds remains independent of the oscillations in a and X. On the other hand, if the rate of reaction through which the flux of R is occurring is made to oscillate, i.e., if 0(t) oscillates, will be a function of this oscillation. If... 

This means that, under conditions of catabolite limitation, Eqn. 70 will give the most easily interpretable relation. Conversely, under anabolite limitation, Eqn. 71 will be the most practical. Both equations predict a linear relation between rate of substrate utilization and biomass formation. Furthermore, the relation between catabolism and anabolism has a positive intersection point with the ordinate. This positive catabolism at (extrapolated) zero growth rate has been interpreted as maintenance energy requirement [52]. It follows naturally from the simple description of bacterial metabolism as we have used it here. 

In contrast, anabolism, often referred to as biosynthesis, consumes energy, rather than producing it, typically taking more oxidised molecules and transforming them into more complex, more highly reduced end products. The reverse process to that described in Equation (1), carried out by many photosynthetic organisms, involves the fixation of atmospheric CO2 to form glucose, catalysed by the enzymes which constitute the Calvin cycle ... 

The project was started with an existing model of metabolism in the cow, published and validated (Baldwin et al., 1987 referred to as Molly), which describes utilization of glucose, amino acids and fatty acids by muscle, adipose, visceral and mammary tissues at an aggregated metabolic pathway level. Elements of genetic background, response to nutritional environment and metabolic hormones are exphcitly embodied in equation forms and parameter values, such as maximal velocity, substrate sensitivity and control by anabolic and catabolic hormones. 

A growth-process equation as a whole represents metabolism, and is the sum of the equations representing the other processes that take place concurrently. For the heterotrophic growth exhibited by yeasts, these latter can be regarded most simply as the processes of anabolism, which is cellular synthesis, and of catabolism, which provides the energy to bring about anabolism. A part of the substrate is utilized as... 

With anaerobic growth processes there will be organic products other than the cells. Each of these must be known as to kind and quantity, and each can be treated in exactly the same manner as the cells in anabolism. There is thus no oxygen involved in any anaerobic equations. The quantity of substrate utilized to form other organic products of a growth-process is calculated in the same manner as the cells, as shown in the following equation. 

The brief description given above on the construction of growth process equations is intended to give some idea of the overall aspects of what goes on when cells are grown. It is not necessary to go through the construction of anabolic and catabolic process equations if one is interested only in metabolism. Once the kinds and quantities of the organic reactants and products of metabolism are known (as... 

The heat production during respiration of glucose is equal to -469 kJ/ mol O2 (with the conditions given in the above equation). In order to produce 3.60 C-mol of biomass, 2.40 mol O2 is consumed in the catabolic reaction. At the same time 0.36 mol O2 is produced (by this way of separating anabolism and catabolism) in the anabolic reaction. Consequently the heat yield could be calculated according to ... 

However, the excess NADH formed due to anabolic reactions has to be taken into account under anaerobic conditions. For instance, S. cerevisiae uses glycerol formation as a way of disposing a surplus of NADH anaerobically [45-47] and this will of course affect the heat production. By using the value of 0.3 mol NADH per C-mol biomass formed [43], the growth equations will change to ... 

Using growing CHO 320 cells as the example of the advocated method, the growth reaction given in Equation (13) is divided into two half-reactions, namely the catabolic half-reaction. Equation (18), and the anabolic half-reaction. Equation (19),... 

The criteria for the separation are well-established (see Reference [105] for details) but, for the genetically engineered cells used in this example, the anabolic half-reaction is taken to include both (i) substrate degradation to form biosynthetic precursors and (ii) the subsequent syntheses from them of the diverse macroinolecules constituting the biomass and the heterologous protein, IFN-y. For the reason stated in Section 5 2.4, carbon dioxide was incorporated into the right hand side of this half-reaction, together with the consequent H2O. Equation (19) implicitly involves the relation [105],... 

The enthalpy change for the anabolic half-reaction is neglected on good circumstantial evidence for microbes reviewed in References [18,105], In one case, it can be seen from the calculations that there is a small but significant enthalpy of anabolism for cultured Saccharoniyces ccrevisiac cells [27] but, even so, the assumption in Equation (20) would only fail by a few percent. 

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