Proteins are one of the essential components of living systems. Along with nucleic acids, polysaccharides, and lipids, proteins constitute the macromolecules that have important roles in biology. Nucleic acids, in the form of DNA and RNA, store and distribute the genetic information as needed. Of particular importance is the information that determines the sequences of amino acids that characterize the proteins. Proteins contribute to the structure of an organism and execute most of the tasks required for it to function. Proteins even form part of the complex mechanism by which they are synthesized. Polysaccharides, linear and branched-chain polymers of sugars, provide structural elements, store energy, and when combined with peptides or proteins, play an important role in antigenicity and, more generally, in cellular recognition. Lipids, which include molecules such as fatty acids, phospholipids, and cholesterol, serve as energy sources and are the most important components of the membrane structures that organize and compartmentalize cellular function.
In this volume we concentrate on globular proteins, the biological macromolecules with the greatest functional range. It is for these systems that the relation of function to structure and dynamics is best understood. Most chemical transformations that occur in living systems are catalyzed by enzymes, the globular proteins that have evolved for executing such specific tasks. As well as enhancing the rates of reactions, sometimes by eight or more orders of magnitude, globular proteins (e.g., repressors) inhibit certain reactions (e.g., the transcription of DNA) involved in the mechanism for the control of growth and differentiation. A breakdown of these control mechanisms can lead to unobstructed growth and the development of cancer. Other proteins (such as hemoglobin) serve to transport small molecules (such as oxygen), electrons, and energy to the appropriate parts of the organism. Antibody molecules are proteins that protect the organism by specifically recognizing and binding to foreign antigenic substances (such as viruses). Many proteins have structural roles; e.g., fibrous tissue is composed mainly of the protein collagen, and the major functional components of muscle, actin and myosin, are proteins.
Because of this wide range of protein functions and the need to develop 1