This book is written for students who are taking their first and perhaps their only course in biochemistry, whether as undergraduates or as graduate or medical students. I undertook this task because I want to convey to students my picture of what this science has recently become. Biochemistry is no longer a mere catalog of the biological occurrence and enzymatic reactions of a large number of organic compounds. In the last few years it has acquired, along with many new facts, a set of organizing principles which have made it a much simpler field to comprehend, and, at the same time, a more powerful way of analyzing many important problems in biology.

How has this come about? Each field of scientific study at some time in its evolution undergoes a profound transition in which a collection of widely scattered facts and hypotheses crystallizes into a logical pattern, unified by a few basic concepts. Biochemistry has been undergoing such a transition, stimulated by new experimental findings and new insights. Among these are the recognition of the principles of energy transfer in cells, the mechanisms by which the major metabolic pathways are regulated, the importance of membranes, ribosomes, and other ultrastructural elements of cells in their molecular activities, and the far-reaching conclusion that the amino acid sequence determines the three-dimensional conformation of protein molecules and thus their biological functions. The new knowledge of the molecular basis of genetics, which has transformed all of biology, has had the most profound influence. Because of these developments biochemistry now has a central story, a leitmotiv, which I have tried to express in simple terms in the Introduction.

This book is concerned primarily with biochemistry at the cell level, where its organizing principles are most clearly evident. Central concepts are emphasized rather than an encyclopedic treatment of biochemical details. There are four major parts in the book:

1. Biomolecules
2. Energy-yielding processes
3. Energy-requiring processes
4. Transfer of genetic information

These are subdivided into what I believe is a logical progression of chapters, each of which is a manageable "package" for both students and teachers, equivalent to the content of one lecture or discussion period. I agree with many teachers that the structure and properties of some biomolecules may best be taught together with their metabolism. This approach is quite feasible using this book, although for student convenience I have chosen to collect most of the material on the structure, chemistry, and occurrence of the various types of biomolecules into one section. I believe this makes for easy reference, while still allowing for flexibility of approach.

Biochemistry has many new frontiers today. I have tried to sketch out some of the most promising in chapters on the regulation of protein synthesis and its role in cell differentiation, the molecular basis of self-assembly and morphogenesis, and the origin of life. These chapters may well be out-of-date soon, but I hope they will serve to acquaint students with some of the biochemistry of the future.

Acknowledgments

Many may think it foolhardy for a single author to attempt to write a comprehensive textbook of biochemistry. However, my publishers have made it possible to enlist the criticism and advice of a number of chemists, biochemists, and biologists expert in research and/or teaching in the areas covered by the book. Each chapter has been read and criticized by at least one and often several authorities. To them I owe a great deal, not only for kind encouragement and sometimes deservedly blunt criticism, but also for the insight and perspective that only the real expert can convey. It is perhaps inevitable that some errors of fact, interpretation, or emphasis will be found, but I trust no one will attribute these to anyone but me. I will greatly appreciate receiving from students and teachers alike their comments, criticisms, notice of errors, and advice about improvements that can be made in later printings or editions.

To the following reviewers I give my most sincere thanks: Jay Martin Anderson, Christian B. Anfinsen, Robert E. Beyer, R. G. S. Bidwell, Rodney L. Biltonen, Konrad E. Bloch, Benjamin Bouck, Daniel Branton, Robert H. Burris, Melvin Calvin, Roderick K. Clayton, Helena Curtis, Robert E. Davies, Bernard D. Davis, John T. Edsall, Paul T. Englund, Allan H. Fenselau, J. Lawrence Fox, Richard Goldsby, Ursula Johnson Goodenough, Guido Guidotti, Gordon G. Hammes, William F. Harrington, Edward C. Heath, Harold G. Hempling, Donald P. Hollis, Lloyd L. Ingraham, Andre T. Jagendorf, William P. Jencks, Daniel E. Koshland, Jr., Sir Hans A. Krebs, Myron Ledbetter, William J. Lennarz, Richard C. Lewontin, Julius Marmur, Daniel Nathans, Leslie Orgel, Peter L. Pedersen, Keith R. Porter, David Prescott, John Sinclair, Gunther Stent, Jack L. Strominger, Maurice Sussman, Serge N. Timasheff, and William B. Wood. My thanks go to many others, acknowledged at the end of the book, who generously gave me permission to use drawings, electron micrographs, and other illustrative material.

I am also grateful to the officers and staff of Worth Publishers for their genuine interest in the needs of both students and teachers, their appreciation of the struggles of a university author, and above all, their desire to produce an educationally useful book.

My colleagues in the Department of Physiological Chemistry of The Johns Hopkins School of Medicine furnished much advice and also took on many responsibilities which the gestation of this book had forced neglect. I also owe a great deal to Johns Hopkins medical students, who taught me whatever I have learned at teaching. Two of them, Bill Scott and Penny Pate, gave me much help in the early stages of preparation of the manuscript; one happy outcome is that they are now Mr. Mrs. William Wallace Scott, Jr. To Linda Hansford I am particularly indebted for invaluable help with proofreading, indexing, checking of problems, and coll of data and references. Thanks also to Ronald Garrett, who photographed the molecular models and to my secretary Peggy Ford, who not only effectively marshalled my time and attention among teaching, research, departmental administration, and book-writing, but also typed many chapters of the manuscript.

Finally, I want to express my deep appreciation to my family, who patiently endured the many weekends and evenings that were devoted to writing and who gave encouragement when it was most needed.

ALBERT L. LEHNINGER, Sparks, Maryland
March, 1970