The Regulation of Metabolisms

Abstract

In a cell, the fluxes of matter and energy are highly controlled so that cells can maintain their organization and multiply when needed. We have discussed in the previous chapter that consecutive reactions can be driven through coupling favorable reactions to unfavorable reactions, many of those benefiting from the ΔG ^o of ATP hydrolysis. Synthesizing ATP involves using energy associated to the chemical processing of nutrients or dedicated molecules stored for this purpose (catabolic metabolism). When in excess, the nutrients tend to engage series of reactions whose end products are the storage molecules (anabolic metabolism) for later use. This shift implies a complex network of metabolisms that have to be inhibited or activated. Inhibition and activation occur selectively at specific reactions which in turn occur in specific locations and precise timings inside cells. In addition, it requires that different cells in the same tissue or in different tissues operate coordinately. Liver, adipose tissue, muscle, and brain, for instance, need to be coordinated so that when the brain and muscle need specific nutrients to operate, this process does not conflict with processes in other organs and no failure of the body function as a whole occurs.