CHAPTER 2Cell Chemistry and Bioenergetics

It is at first sight difficult to accept the idea that living creatures are merely chemical systems. Their incredible diversity of form, their seemingly purposeful behavior, and their ability to grow and reproduce all seem to set them apart from the world of solids, liquids, and gases that chemistry normally describes. Indeed, until the late nineteenth century, animals were generally believed to contain a Vital Force—an “animus”—that was responsible for their distinctive properties.

We now know that there is nothing in living organisms that disobeys chemical or physical laws. However, the chemistry of life is indeed special. First, life depends on chemical reactions that take place in aqueous solution, and it is based overwhelmingly on carbon compounds, the study of which is known as organic chemistry. Second, although cells contain a variety of small carbon-containing molecules, most of the carbon atoms present are incorporated into enormous polymeric molecules—chains of chemical subunits linked end-to-end. It is the unique properties of these macromolecules that enable cells and organisms to grow and reproduce—and to do all the other things that are characteristic of life. Third, and most important, cell chemistry is enormously complex: even the simplest cell is vastly more complicated in its chemistry than any other chemical system known. In fact, we now recognize that the many interlinked networks of chemical reactions in cells can give rise to so-called emergent properties, which will require the development of new experimental and computational methods to understand.

Much of the information in this chapter is summarized—and in some cases further elaborated—in the nine two-page Panels with which the chapter ends (Panels 2–1 to 2–9). Although the Panels will be cited at appropriate places in the text, they should also be useful for refreshing background knowledge when reading later chapters.