The same principles, largely intact, must suffice to explain and predict the properties of the larger molecules. Rigorous physical theory and powerful experimental techniques already provide a deep understanding of the properties of small molecules. They derive from basic molecular physics and chemistry. Unlike the rest of biology, structural biology is in the unique position of having its unifying principles largely known. The richness and diversity of biological phenomena have led to the danger of a biology overwhelmed with descriptions of phenomena and devoid of any unifying principles. A curious phenomenon in some living organism sparks our interest, perhaps because it is reminiscent of some previously known phenomenon, perhaps because it is inexplicable in any terms currently available to us. Much of biological research still begins as descriptive science. Because of recent advances, primarily in recombinant DNA technology, computer science, and biological instrumentation, we should begin to realize the goals of structural biology during the next two decades.

Although we are still a long way from these goals, enormous progress has been made during the past two decades. The ultimate goals of this field are to be able to predict the structure, function, and behavior of the machines from their chemical formulas, through the use of basic principles of chemistry and physics and knowledge derived from studies of other machines. The field of structural biology is concerned with the properties and behavior of the machines themselves.

Many areas of biological science focus on the signals detected by these machines or the output from these machines. Included are proteins, nucleic acids, carbohydrates, lipids, and complexes of them.

These events are directed, modulated, or detected by complex biological machines, which are themselves large molecules or clusters of molecules. All biological functions depend on events that occur at the molecular level.

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