BIOCHEMISTRY

the field of science concerned with the chemical substances and processes that occur in plants, animals, and microorganisms. Specifically, it involves the quantitative determination and structural analysis of the organic compounds that comprise the basic constituents of cells (proteins, carbohydrates, and lipids) and of those that play a key role in chemical reactions vital to life (nucleic acids, vitamins, and hormones). Biochemistry entails the study of all the complexly interrelated chemical changes that occur within the celle.g., those relating to protein synthesis, the conversion of food to energy, and the transmission of hereditary characteristics. Both the cell's degradation of substances that release energy and its buildup of complex molecules that store energy or act as substrates or catalysts for biological chemical reactions are studied in detail by biochemists. Biochemists also study the regulatory mechanisms within the body that govern these and other processes. Biochemistry lies in the border area between the biological and physical sciences. Accordingly, it makes use of many of the techniques common to physiology and those integral to analytical, organic, and physical chemistry. The field of biochemistry has become so large that many subspecialities are recognized, as, for example, clinical chemistry and nutrition. Molecular biology, the study of large moleculesfor example, proteins, nucleic acids, and carbohydratesthat are essential to life processes is a field closely allied to biochemistry. Taken as a whole, modern biochemistry has outgrown its earlier status of an applied science and has acquired a place among the pure, or theoretical, sciences. Biochemistry is treated in a number of articles. For the history and principal treatment of the discipline, see biochemistry. For the primary subjects of study, see carbohydrate; hormone; lipid; nucleic acid; protein; vitamin; chemical compound; cell; heredity; genetics; metabolism; photosynthesis. For basic methodology and instrumentation, see analysis. study of the chemical substances and processes that occur in plants, animals, and microorganisms and of the changes they undergo during development and life. It deals with the chemistry of life, and as such it draws on the techniques of analytical, organic, and physical chemistry, as well as those of physiologists concerned with the molecular basis of vital processes. All chemical changes within the organismeither the degradation of substances, generally to gain necessary energy, or the buildup of complex molecules necessary for life processesare collectively termed metabolism. These chemical changes depend on the action of organic catalysts known as enzymes, and enzymes, in turn, depend for their existence on the genetic apparatus of the cell. It is not surprising, therefore, that biochemistry enters into the investigation of chemical changes in disease, drug action, and other aspects of medicine, as well as in nutrition, genetics, and agriculture. The term biochemistry is synonymous with two somewhat older terms: physiological chemistry and biological chemistry. Those aspects of biochemistry that deal with the chemistry and function of very large molecules (e.g., proteins and nucleic acids) are often grouped under the term molecular biology. Biochemistry is a young science, having been known under that term only since about 1900. Its origins, however, can be traced much further back; its early history is part of the early history of both physiology and chemistry. Additional reading Overviews are provided by Thomas M. Devlin (ed.), Textbook of Biochemistry: With Clinical Correlation, 3rd ed. (1992), a good general textbook for medical and graduate students; Lubert Stryer, Biochemistry, 4th ed. (1995), with excellent illustrations; Albert L. Lehninger, David L. Nelson, and Michael M. Cox, Principles of Biochemistry, 2nd ed. (1993); and J. David Rawn, Biochemistry, international ed. (1989), a strong text still of great utility. Joseph Needham (ed.), The Chemistry of Life: Eight Lectures on the History of Biochemistry (1970), provides a brief development of the important areas of photosynthesis, enzymes, microbiology, neurology, hormones, vitamins, and other topics. Frederic Lawrence Holmes, Hans Krebs, 2 vol. (199193), is a dense biography of one of the founders of modern biochemistry. Robert E. Kohler, From Medical Chemistry to Biochemistry (1982), compares the growth of the discipline in the United States, Britain, and Germany.Particular topics are addressed in J. Etienne-Decant and F. Millot, Genetic Biochemistry: From Gene to Protein (1988; originally published in French, 1987), an overview of information flow from genes to proteins; Maria C. Lindner (ed.), Nutritional Biochemistry and Metabolism: With Clinical Applications, 2nd ed. (1991), on the dynamic roles that nutrients play in the structure and function of the human body; and P.K. Stumpf and E.E. Conn (eds.), The Biochemistry of Plants: A Comprehensive Treatise (1980 ). Richard E. Dickerson and Irving Geis, The Structure and Action of Proteins (1969), treats one of the essential types of biochemical molecules used by cells. Proteins and other molecules also are described and illustrated in Linus Pauling and Roger Hayward, The Architecture of Molecules (1964).The subject of endocrinology has changed markedly amid the genetic revolution. A reliable work on this topic is Franklyn F. Bolander, Molecular Endocrinology, 2nd ed. (1994). D.G. Hardie, Biochemical Messengers: Hormones, Neurotransmitters, and Growth Factors (1991), also includes coverage of other signaling devices that have evolved at the molecular level. Elmer H. Stotz Birgit Vennesland The Editors of the Encyclopdia Britannica