Overview

Investigation of the chemistry of life had begun in the nineteenth century with the discovery that organic molecules, the chemicals found in living things, were larger and more complex than inorganic molecules, those in the non-living world. By the end of the century, the major classes of organic molecules—the carbohydrates, lipids, proteins, and nucleic acids—had all been identified, but little was known about the cellular processes involved in making and breaking them down. Metabolism is a general term for the sum of all the chemical reactions that make up these processes. During the first half of the twentieth century, biochemists and biologists began to make significant progress in working out the steps in these chemical reactions, which turned out to be much more complex than had been originally suspected. The study of the...