Pathways Show Functional Coupling

Large metabolic charts have been designed to display all the major biochemical pathways. Such charts present a bewildering array of interconnected pathways, making it difficult to appreciate relationships between different pathways. The overall operational aspects of metabolism may be clarified by simpler block diagrams that omit details and focus on functional relationships. Such a functional block diagram for a typical heterotrophic aerobic cell is shown in figure 11.4. The metabolism of such a system is symbolized by two functional blocks  

Catabolism or degradative metabolism. Foods are oxidized to carbon dioxide. Most of the electrons liberated in this oxidation are transferred to oxygen, with concomitant production of ATP (electron-transfer phosphorylation). Other electrons are used in the regeneration of NADPH, the most frequently used reducing agent for biosynthesis. The major pathways in this block are the glycolytic sequence and the tricarboxylic acid (TCA) 

Another way of looking at metabolism, which emphasizes the precursor-product relationship, is depicted in figure 11.5. Here metabolism is pictured as three concentric boxes. The inner box shows the central metabolic pathways and the interconversions of various small molecules. These substances serve as the starting materials for all other metabolism. Some of the compounds formed from these intermediates are shown in the middle concentric box. These 

In analyzing metabolism we must distinguish between a sequence and a conversion. A conversion might be the transformation of starting material A to end product Z a sequence is the specific set of reactions by which such a conversion is carried out. The conversion of glucose to pyruvate involves a ten-step sequence (see figures 11.2 and 

In fact any conversion can be made thermodynamically favorable by coupling it to a sufficient number of ATP-to-ADP conversions. This strategy is exploited in the design of metabolically paired sequences. A simple example is the interconversion of fructose-1,6-bisphosphate (F-l, 6-bisP) into fructose-6-phosphate (F-6-P). This is the simplest possible type of interconversion since it involves only one reaction in either direction (fig. 11.6). 

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Organisms Differ in Sources of Energy, Reducing Power, and Starting Materials for Biosynthesis Reactions Are Organized into Sequences or Pathways Sequentially Related Enzymes Are Frequently Clustered Pathways Show Functional Coupling The ATP-ADP System Mediates Conversions in Both Directions... 

Figure 2 Pulse sequences and coherence pathway diagrams for the phase-modulated split-t) (A) STMAS and (B) triple-quantum MAS NMR, showing the generic sequences with the specific values for Mg being r=24/31, r —O, r"=7/31 and s=12/31, s =0, s"— 9/3 and (C) numerical simulations of the relative sensitivity of the ST and MQ experiments as a function of the ratio between the RF field strength and the quadrupolar coupling...

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