This book was written, to a not inconsiderable degree, on the basis of the course "The Problems of Modern Biophysics" which the author gives to the students and postgraduates of the Biophysical Department at Moscow University School of Physics. It is meant for those who have a sufficiently good background in physics as well as in biology. I have tried to make this book intelligible to a broader circle of readers, i.e., to physicists not competent enough in biology, and to biologists not competent enough in physics. I hope that I have succeeded. This book is neither a textbook nor a systematic account of a field of science. I think that in modern biological physics, i.e., in the branch of biology where people having fundamental physical or physico-chemical education are working, so many specific answers have been recently obtained that it is now just the right time to ask at least several questions of a general nature. The aim of this book is to formulate such questions though their choice is, to a considerable degree, determined by the authors preferences and interests.

This book is aimed at a large audience: from students, who have a high- school background in physics, mathematics, chemistry, and biology, to scien- tists working in the fields of biophysics and biochemistry. The main aim of this book is to attempt to describe, in terms of physical chemistry and chemi- cal physics, the peculiar features of "machines" having molecular dimen- sions which play a crucial role in the most important biological processes, viz. , energy transduction and enzyme catalysis. One of the purposes of this book is to analyze the physical background of the high efficiency of molecu- lar machines functioning in the living cell. This book begins with a brief review of the subject (Chapter 1). Macro- molecular energy-transducing complexes operate with thermal, chemical, and mechanical energy, therefore the appropriate framework to discuss the functioning of biopolymers comes from thermodynamics and chemical kinet- ics. That is why we start our analysis with a consideration of the conventional approaches of thermodynamics and classical chemical kinetics, and their application to the description of bioenergetic processes (Chapter 2). Critical analysis of these approaches has led us to the conclusion that the conven- tional approaches of physical chemistry to the description of the functioning of individual macromolecular devices, in many cases, appear to be incom- plete. This prompted us to consider the general principles ofliving machinery from another point of view.