1. Introduction

La inspiración existe, pero tiene
que encontrarte trabajando.

Pablo Ruiz Picasso (1881-1973)

The scientist is not a person
who gives the right answers, he
is one who asks the right

Claude Lévi-Strauss (1908-2009)

Most scientists agree that research requires imagination and tenacity. Once these two virtues are gathered, the discovery of a breakthrough is a matter of luck. Nevertheless, the history of science is not only made of breakthroughs. Instead, it is made of discoveries of different importance. Some discoveries just represent a little expansion of our knowledge. Nowadays, the frontiers of the science are expanded at the highest rate ever, thanks to millions of researchers from all over the world. However, science is not a collection of phenomena. It is also a frame to interpret the results. Therefore, all the little investigations need to be unified from time to time. Precisely, this is what great scientists do. For instance, Isaac Newton unified the celestial and the terrestrial mechanics in his book Principia. Indeed, a new paradigm usually provides a simplified way to look at phenomena and establishes a landmark to promote new investigations.

In 1828, the German chemist Friederich Wöhler accidentally unified the chemistry and the biology with a simple experiment. The experiment consisted in a chemical reaction in which two inorganic substances (silver cyanate and ammonium chloride) were mixed to produce an organic composite (urea). At that time, scientists believed that the inanimate (inorganic) matter was fundamentally different from the living (organic) matter. Wöhler's discovery was followed by other experiments supporting his observations. The scientists finally convinced themselves that both types of matter were made of atoms and there was no intrinsic difference between them. In 1903, the German scientist Carl Neuberg coined the word Biochemistry, to refer to a new discipline that studied the processes of life (respiration, fermentation, etc.) from a chemical point of view.

The birth of biophysics was not that straightforward. Instead, it took decades to clarify whether physics could be used to answer biological questions [31]. In the mid 19th century, the School of Berlin was a group of scientists who firstly applied physics to the study of living systems. They strongly believed that physiology (i.e., the functioning of living systems) could be regarded as physical phenomena. For instance, Emil DuBois-Reymond modeled the nerves as an electrical system. Another example is Carl Ludwig, who firstly measured the blood pressure. This scientific discipline was known as medical physics. However, it remained in standby because the physics of the 19th century could not provide explanations to all phenomena observed. In 1944, Erwin Schrödinger, the Austrian physicist who co-formulated the dynamics of quantum systems, wrote an inspiring book entitled What Is Life? [32]. The book essentially suggested a physical approach to the questions concerning biology. In 1953, Watson and Crick discovered the double-helix structure of DNA (i.e., one of the most significant molecules in biology) by using X-ray diffraction (i.e., an experimental technique developed by physicists) [1]. This achievement represents the starting point of modern biophysics, which mainly focused on the structure and interaction of biomolecules and cells. Finally, the single-molecule techniques developed during the last decade of the 20th century represented a new revolution in the field of biophysics [33].

Figure 1.1: Portrait of Friederich Wöhler (1800-1882), who discovered that urea (organic matter) could be synthesized from inorganic matter (left picture). James Watson and Francis Crick showing the double-helix structure of DNA in 1953 (right picture).

The aim of this chapter is to focus the object of study of this thesis. We will overview the questions of interest in biophysics; we will state the scope of this work within the field of biophysics; and we will summarize the main results presented here.

JM Huguet 2014-02-12