1.1 What is biophysics?

Biophysics is a scientific discipline that uses the tools and the methods of physics to study biological systems [34,35]. In other words, biophysics is the study of physical processes governing the living cells. This general definition includes a variety of subtopics that focus on a wide range of levels, from molecular processes to ecological phenomena. Biophysicists also look at several aspects of biological systems such as structure, dynamics, mechanisms, complexity, applications, etc.

Figure 1.2: Some topics in biophysics. (a) Molecular biophysics. Structure of a DNA polymerase [36]. Picture of Protein Data Bank ID: 1TAU, created with PyMOL software (DeLano Scientific, 2002). (b) Cellular biophysics. Schematic representation of a cell. (c) Systems biology. A network of genes and their interaction.

The term biophysics is the result of mixing the words biology and physics. This suggests that both branches of knowledge are blended into a new discipline. However, the skills required in biology are very different from the ones required in physics. So the intersection between them is minimal. Indeed, biology is descriptive and complex, while physics is conceptual and simplistic. Biology is worried about the details, while physics tends to establish general laws. How can both ways reconcile?

A traditional answer to this question proposes either a biological or a physical approach to biophysics [37]. In the first case, physics is the servant to study a biological problem. Physicists contribute to biology by providing experimental techniques and mathematical tools. In the second case, the biologist provides a system that is studied by physicists like any other physical system. The physicist tries to find and understand new physical phenomena to establish new concepts and laws. Although the difference between both approaches seems fuzzy, there is a central question that clarifies this. Who benefits from research in biophysics? If the answer is biology, we are facing a biological approach. Otherwise, this is a physical approach. Let us focus on two examples.

Still, there are reluctances in the collaboration between physicists and biologists. Some biologists dislike the simplistic approach of physicists and prefer not to get rid of details. Some physicists consider that biosystems are too complicated for calculations. In fact, physicists feel much more attracted by biology. Indeed, they discover new phenomena where physical laws can be applied.

Nevertheless, this dual approach to biophysics is being left behind. Universities from all over the world devote degrees, masters, PhD programs and professors exclusively to biophysics. Besides, research institutes are created as a response to the demands of biophysics. All these efforts are changing the way we look at biophysics. Biophysics is no longer "physics for biologists" or "physicals methods applied to biology". On the contrary, biophysics is a discipline defined by its own scientific questions [41]. Biophysicists have become a new kind of researchers. They do not want to explain the biological processes in exact detail nor with an ideal model. They face scientific issues by extracting general laws of biological systems without excessive simplification.

Biophysics is closely related with other disciplines such as biochemistry, nanotechnology or biomedicine. The border among them is not sharp. Rather, there is an overlapping of topics, experimental techniques and theoretical frameworks. Though, the most significant feature of biophysics is the use of measurements and quantitative information.

JM Huguet 2014-02-12