The Fires of Life - cell metabolism

Whole Earth,  Winter, 1999  by Harold J. Morowitz

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Starting with one sugar glucose molecule, it takes eleven steps and eight enzymes to bring us to two molecules of acetic acid. Each acid then enters a cell cycle where it is completely "burned" (oxidized) to carbon dioxide and a spectacular product of energy-rich, hydrogen-rich molecules. The carbon dioxide is released to the environment and the molecules of the energy-rich ATP are made available to the cell.

At this stage, the hydrogen-rich compounds go through still another series often reactions and enzymes, ultimately combining the hydrogen with oxygen to form water. The sugar has now been completely combusted to carbon dioxide and water. The energy from the final oxidation is used to charge up a proton storage cell. This stored energy is used to make many more ATPs, the ubiquitous energy-transfer molecules. So the slow burning of sugar in cells converts a good deal of the energy of the reaction into a form to do biological work.

Without the Inner Fire, No Life

The central reactions of cellular metabolism go back some four billion years, to all life's universal ancestor--which originally operated in the absence of oxygen. The ancestor's energy came from chemicals bubbling up from the magma just below the surface of the earth. Then, about two billion years ago, photosynthetic organisms started to build up our rich oxygen atmosphere. At this point some cells learned how to use the oxygen for energy, employing familiar chemical pathways but running them in the opposite direction. Invisible, internal, cellular fire entered the world. As the biosphere's oxygen concentration increased, the flash point lowered and ordinary, visible biomass fire appeared. After photosynthesis took over as the primary energy source for biomass fuels, all earthly combustion became a gift from the fiery sun. And so it has been for the last two billion years.

The earth, water, air, and fire of the ancients are the lithosphere, hydrosphere, atmosphere, and biosphere of today's geochemists. Without the last of these, there would be no fire.

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COPYRIGHT 1999 Point Foundation
COPYRIGHT 2000 Gale Group