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Chemical Components of Cells

At first sight, it is difficult to comprehend 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, it was widely believed that all living things contained a vital force—an “animus”—that was responsible for their distinctive properties.

We now know that there is nothing in a living organism that defies chemical or physical laws. However, the chemistry of life is indeed a special kind. First, it is based overwhelmingly on carbon compounds, the study of which is known as organic chemistry. Second, it depends almost exclusively on chemical reactions that take place in a water-based, or aqueous, environment and in the relatively narrow range of temperatures experienced on Earth. Third, it is enormously complex: even the simplest cell is vastly more complicated in its chemistry than any other chemical system known. Fourth, it is dominated and coordinated by collections of large polymers—molecules made of many chemical subunits linked end to end—whose unique properties enable cells and organisms to grow and reproduce and to do all the other things that are characteristic of life. Finally, the chemistry of life is tightly regulated: cells deploy a wide variety of mechanisms to make sure that each of their chemical reactions occurs at the proper rate, time, and place.

In this chapter, we briefly survey the chemistry of the living cell. We will meet the molecules from which cells are made and examine their structures, shapes, and chemical properties. Because this information is so fundamental to our understanding of cell biology, this chapter includes a set of review panels in which we summarize the key features of the molecules found in cells and the forces that govern their interactions (Panels 2–1 to 2–7, pp. 70–83). We will refer to these panels, which provide a reference guide to life's special chemistry, throughout this chapter—and the entire book. By studying these molecules and their interactions, we can begin to see how cells exploit the laws of chemistry and physics to survive, thrive, and reproduce.