Energy ATP and

Fig. 5.15. Anabolic pathways (synthetic) and central catabolic pathways 14. Only the main biosynthetic routes, and their principal connections to catabolic routes, are shown, in simplified version. The relationships between energy (ATP), and redox (NAD4, NADP ) metabolism, nitrogen...

A schematic block diagram of the metabolism of a typical aerobic heterotroph. The block labeled Catabolism represents pathways by which nutrients are converted to small-molecule starting materials for biosynthetic processes. Catabolism also supplies the energy (ATP) and reducing power (NADPH) needed for activities that occur in the second block these compounds shuttle between the two boxes. The block labeled Biosynthesis represents the synthesis of low- to medium-molecular-weight components of the cell as well as the synthesis of proteins, nucleic acids, lipids, and carbohydrates and the assembly of membranes, organelles, and the other structures of the cell. 

The upshot on the oscillation is a direct measure for the extent of perturbation on the metabolic network upon the uptake of a PAC. Glycolytic oscillations that are systematically perturbed by altered environmental conditions, i.e. exposure to the xenobiotic, constitute a direct and easily accessible measure of the intracellular behavior since the frequency and amplitude of oscillating metabolite concentrations and fluxes depend on both the perturbation and on most intracellular processes due to the coupled energy (ATP) and redox (NADH) balances (Fig. 3.4). 

Nucleotides play central roles in metabolism. They serve as sources of chemical energy (ATP and guanosine triphosphate (GTP)), participate in cellular signalling (cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP)) and are incorporated into important cofactors of enzymatic reactions. Nucleotides are molecules that, when joined together, make up the structural units of RNA and DNA (Scheme 3). 

Fig. 10.9. Role of malic acid in the production of energy (ATP) and the formation of different substrates in the grape (Ruffner, 1982b). MDH, malate dehydrogenase ME, malic enzyme PEPC, phosphoenolpyruvate carboxylase PEPCK, phosphoenolpyruvate carboxykinase...

Fig. 2. Conformational free energy of closed, intermediate and open protein kinase conformations. cAPK indicates the unbound form of cAMP-dependent protein kinase, cAPKiATP the binary complex of cAPK with ATP, cAPKiPKP the binary complex of cAPK with the peptide inhibitor PKI(5-24), and cAPK PKI ATP the ternary complex of cAPK with ATP and PKI(5-24). Shown are averaged values for the three crystal structures lATP.pdb, ICDKA.pdb, and ICDKB.pdb. All values have been normalized with respect to the free energy of the closed conformations.

ATP IS the mam energy storing molecule for practically every form of life on earth We often speak of ATP as a high energy compound and its P—O bonds as high energy bonds This topic is discussed m more detail m Sections 28 4 and 28 5... 

Adenosine triphosphate (ATP) is a key compound m biological energy storage and delivery... 

Active Transport. Maintenance of the appropriate concentrations of K" and Na" in the intra- and extracellular fluids involves active transport, ie, a process requiring energy (53). Sodium ion in the extracellular fluid (0.136—0.145 AfNa" ) diffuses passively and continuously into the intracellular fluid (<0.01 M Na" ) and must be removed. This sodium ion is pumped from the intracellular to the extracellular fluid, while K" is pumped from the extracellular (ca 0.004 M K" ) to the intracellular fluid (ca 0.14 M K" ) (53—55). The energy for these processes is provided by hydrolysis of adenosine triphosphate (ATP) and requires the enzyme Na" -K" ATPase, a membrane-bound enzyme which is widely distributed in the body. In some cells, eg, brain and kidney, 60—70 wt % of the ATP is used to maintain the required Na" -K" distribution. 

FIGURE 1.3 ATP and NADPH, two biochemically important energy-rich compounds. 

Similarly, the release of free energy that occurs upon the hydrolysis of ATP and other high-energy phosphates can be treated quantitatively in terms of group transfer. It is common to write for the hydrolysis of ATP... 

For the phosphoric anhydrides, and for most of the high-energy compounds discussed here, there is an additional entropic contribution to the free energy of hydrolysis. Most of the hydrolysis reactions of Table 3.3 result in an increase in the number of molecules in solution. As shown in Figure 3.11, the hydrolysis of ATP (as pH values above 7) creates three species—ADP, inorganic phosphate (Pi), and a hydrogen ion—from only two reactants (ATP and HgO). The entropy of the solution increases because the more particles, the more disordered the system. (This effect is ionization-dependent because, at low pH, the... 

So far, as in Equation (3.33), the hydrolyses of ATP and other high-energy phosphates have been portrayed as simple processes. The situation in a real biological system is far more complex, owing to the operation of several ionic equilibria. First, ATP, ADP, and the other species in Table 3.3 can exist in several different ionization states that must be accounted for in any quantitative analysis. Second, phosphate compounds bind a variety of divalent and monovalent cations with substantial affinity, and the various metal complexes must also be considered in such analyses. Consideration of these special cases makes the quantitative analysis far more realistic. The importance of these multiple equilibria in group transfer reactions is illustrated for the hydrolysis of ATP, but the principles and methods presented are general and can be applied to any similar hydrolysis reaction. 

We can end this discussion of ATP and the other important high-energy compounds in biology by discussing the daily metabolic consumption of ATP by humans. An approximate calculation gives a somewhat surprising and impressive result. Assume that the average adult human consumes approximately... 

Hexokinase catalyzes the phosphorylation of glucose from ATP, yielding glncose-6-P and ADR Using the values of Table 3.3, calculate the standard-state free energy change and equilibrium constant for the hexokinase reaction. 

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