Energy-requiring processes

The production of two molecules of ATP in glycolysis is an energy-requiring process ... 

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 logistics requirements are quite different. Whereas biomass is optimally used when processed decentrally, the power density of solar energy requires processing at large centralized units. 

The energy released is captured in the form of a molecule known as adenosine triphosphate (ATP) and is used to drive all our energy-requiring processes synthesis of complex molecules, movement, nerve conduction, muscle contraction, and so on. 

The formation of aminoacyl-tRNA molecules is an energy-requiring process, which means that some sort of driving force is required to push the reaction to completion. 

Figure 2.8 The ATP/ADP cycle. The major ATP-generating process from fuel oxidation is oxidative phosphorylation driven by electron transport in the mitochondria. In muscle, the major energy-requiring process is physical activity. The phosphate ion is omitted from the figure for the sake of simplicity.

Since the intracellular concentration of most amino acids is considerably greater than that in the plasma (Table 8.2), the transport of these amino acids is an energy-requiring process. This is achieved via the Na+ gradient across the plasma membrane, which is maintained by the ATP-dependent Na pump the NaVK+ ATPase (Figure 8.5). This is similar to that of the transport of glucose across the luminal membranes of epithelial cells in the gut and in the tubules is the kidney cortex. 

At this site, creatine kinase catalyses the phosphorylation of ADP by phosphocreatine with the production of ATP which, in turn, is used by the energy-requiring process that is, the cross-bridge cycle (Chapter 13). 

Nucleosides are also encountered in the structures of adenosine triphosphate (ATP) and coenzyme A (HSCoA). ATP provides nature with its currency unit for energy. Hydrolysis of ATP to adenosine diphosphate (ADP) liberates energy, which can be coupled to energy-requiring processes in biochemistry, and synthesis of ATP from ADP can be coupled to energy-releasing processes (see Box 7.25). 

Temperature-Dependence of Amino Acid Uptake in Soybean. The uptake of amino acids by plants into the soluble pool can be an energy-requiring process (52-54), as is the support of protein synthesis. We wished to show the temperature-dependence of influx of amino acids into soybean trifoliate leaf discs taken from control and ozonated seedlings in order to confirm this for the present system. Table II shows that amino acid influx during 30 min was reduced by the lowered temperature by about 70%, and protein synthesis by about 85%, when labelling of control discs proceeded at ice bath temperatures. Qualitatively similar reductions occurred in discs taken from ozonated (50 5 pphm,... 

Certain molecules, such as p-aminohippuric acid (Fig. 3.18), a metabolite of p-aminobenzoic acid are actively transported from the bloodstream into the tubules by a specific anion transport system. Organic anions and cations appear to be transported by separate transport systems located on the proximal convoluted tubule. Active transport is an energy-requiring process and therefore may be inhibited by metabolic inhibitors, and there may be competitive inhibition between endogenous and foreign compounds. For example, the competitive inhibition of the active excretion of uric acid by compounds such as probenecid may precipitate gout. 

The energy generated by metabolism of the macronutrients is used for three energy-requiring processes that occur in the body resting metabolic rate, thermic effect of food (formerly termed specific dynamic action), and physical activity. 

Three major energy-requiring processes occurring in the body... 

Flow of energy in the biosphere. The sun s rays are the ultimate source of energy. These rays are absorbed and converted into chemical energy (ATP) in the chloroplasts. The chemical energy is used to make carbohydrates from carbon dioxide and water. The energy stored in the carbohydrates is then used, directly or indirectly, to drive all the energy-requiring processes in the biosphere. 

Intermediary metabolism, the synthesis and degradation of small molecules, serves two functions It supplies the energy needed for the synthesis of macromolecules and other energy-requiring processes, and it furnishes these processes... 

There are no active (energy-requiring) processes dominating the distribution. 

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