Metabolism and ATP Energy

In 1961 Bob Williams was the first to point out that the role of hydrogen in biology, in bound and protonic forms, made it the ideal element for coupling both metabolic and proton energies to the formation of ATP. The connection made depended upon his realization of the importance of electron-transfer chains in biology and therefore a fundamental role for iron. A long exchange of views with Dr. P. Mitchell has followed. 

In the body, the energy derived from food is released as body heat and also used in the synthesis of ATP. The energy captured in ATP is then transformed into other forms, i.e., chemical (synthesis of new compounds), mechanical (muscle contraction), electrical (nerve activity), electrochemical (various ion pumps), thermal (maintenance of body temperature), and informational (base sequences in nucleic acids, amino acids in proteins). In general, the energy of food provides for the specific dynamic action of food, the maintenance of the body s basal metabolism, and the energy expenditure associated with various types of activity. 

Fig. 1. Energy transformations in fuel metabolism. When ATP energy is transformed into cellular responses, such as muscle contraction, ATP is cleaved to ADP and Pi (inorganic phosphate). In cellular respiration, O2 is used for regenerating ATP from oxidation of fuels to CO2.

T is 81.0 MHz. Numerous investigations, particularly in the biochcmicaUield. have been based on "P resonance. An example is shovnn in Figure 19-31, The species under study is adenosine triphosphate (ATP), a triply charged anion that plays a vital role in carbohydrate metabolism and in energy storage and release in the bodv. 

The overall free-energy change is given by G° = —31 kJ mol + 29 kJ mol = 2 kJ mol, which means that the coupled reaction now favors the formation of product, and an appreciable amount of alanylglycine will be formed under this condition. Figure 8.14 shows the ATP-ADP interconversions where energy is stored (from metabolism) and free energy is released (from ATP hydrolysis) to drive essential reactions. 

Situated as it is between glycolysis and the electron transport chain, the TCA cycle must be carefully controlled by the ceil. If the cycle were permitted to run unchecked, large amounts of metabolic energy could be wasted in overproduction of reduced coenzymes and ATP conversely, if it ran too slowly, ATP would not be produced rapidly enough to satisfy the needs of the cell. Also, as just seen, the TCA cycle is an important source of precursors for biosynthetic processes and must be able to provide them as needed. 

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