ATP, biosynthesis

Where P/O = is the number of ADP phosphorylations per atom of oxygen consumed. For biosynthesis (ATP utilisation) we can write ... 

Nevertheless the biosynthesis of glutamine proceeds from glutamic acid The dif ference is that the endergonic process m Equation 1 is coupled with the strongly exer gome hydrolysis of ATP... 

Thermodynamic considerations demand that the energy necessary for biosynthesis of any substance exceed the energy available from its catabolism. Otherwise, organisms could achieve the status of perpetual motion machines A few molecules of substrate whose catabolism yielded more ATP than required for its resynthesis would allow the cell to cycle this substance and harvest an endless supply of energy. 

The acetyl-CoA derived from amino acid degradation is normally insufficient for fatty acid biosynthesis, and the acetyl-CoA produced by pyruvate dehydrogenase and by fatty acid oxidation cannot cross the mitochondrial membrane to participate directly in fatty acid synthesis. Instead, acetyl-CoA is linked with oxaloacetate to form citrate, which is transported from the mitochondrial matrix to the cytosol (Figure 25.1). Here it can be converted back into acetyl-CoA and oxaloacetate by ATP-citrate lyase. In this manner, mitochondrial acetyl-CoA becomes the substrate for cytosolic fatty acid synthesis. (Oxaloacetate returns to the mitochondria in the form of either pyruvate or malate, which is then reconverted to acetyl-CoA and oxaloacetate, respectively.)... 

In fatty-acid biosynthesis, a carboxylic acid is activated by reaction with ATP to give an acyl adenylate, which undergoes nucleophilic acyi substitution with the — SH group or coenzyme A. (ATP = adenosine triphosphate AMP = adenosine monophosphate.)... 

Step 1 of Figure 29.13 Carboxylation Gluconeogenesis begins with the carboxyl-afion of pyruvate to yield oxaloacetate. The reaction is catalyzed by pyruvate carboxylase and requires ATP, bicarbonate ion, and the coenzyme biotin, which acts as a carrier to transport CO2 to the enzyme active site. The mechanism is analogous to that of step 3 in fatty-acid biosynthesis (Figure 29.6), in which acetyl CoA is carboxylated to yield malonyl CoA. 

Where biosynthesis of a product requires the net input of energy, the theoretical yield will be influenced by the P/O quotient of the process organism. Furthermore, where the formation of a product is linked to the net production of ATP and/or NADH, the P/O quotient will influence the rate of product formation. It follows that to estimate the potential for yield improvement for a given primary or secondary metabolite, it is necessary to determine the P/O quotient of the producing organism. 

Metabolites whose biosynthesis is energy requiring, for example exopolysaccharides using certain substrates. Here, part of the substrate has to be oxidised to provide ATP for biosynthesis and thus the P/O quotient of the producing organism influences the theoretical yield. 

Metabolites whose biosynthesis leads to the net production of ATP and/or reducing equivalents, for example organic adds and certain secondary metabolites. In these cases, the P/O quotient influences the extent to which energy can be dissipated. 

In dass 3, the rate of metabolite production from a single substrate may be limited by the rate of ATP turnover. Provision of ready made precursors can increase both the metabolite yield (final concentration) and rate of production by decreasing the requirement for ATP turnover during biosynthesis. 

The lower than expected yields can be explained by the nature of methane oxidation to methanol in these bacteria. This reaction, catalysed by methane mono-oxygenase, is a net consumer of reducing equivalents (NADH), which would otherwise be directed to ATP generation and biosynthesis. In simple terms the oxidation of methane to methanol consumes energy, lowering the yield. 

Anabolism is the building up or biosynthesis, of complex molecules such as protein, nucleic adds and polysaccharides, from raw materials originating from intra- or extracellular sources. The biosyntheses are energy (ATP) requiring processes. 

The theoretical limits are 1.0 (all ATP) and 0 (all AMP) with a normal working range of 0.75 to 0.9. The involvement of energy charge in the integration and regulation of metabolism is considered further in die BIOTOL text entitled Biosynthesis and the Integration of Cell Metabolism. ... 

Class 1 or 2, depending on the substrate used. We can see from Table 2, for example, that sucdnoglycan biosynthesis leads to a net production of ATP (Class 2) with ethanol as substrate, but the biosynthesis is energy requiring (Class 1) with glucose as substrate. 

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