Our ambitious goal, through this NetworkPlus proposal, is to bring biologists and physicists together to develop a unified framework for understanding biology that integrates the molecular and the system levels of thinking into a coherent, unified whole. Single molecules may be addressed by reductionist methods, but whole organisms, or ecosystems, present challenges on an entirely different scale, both in terms of the number and diversity of molecular components. Integration of thinking across the length-scales remains very difficult. These kinds of challenges are familiar to physicists. Quantum theory describes the behaviour of sub-atomic particles, while the general theory of relativity describes the motions of galaxies; the quest for a unified theory that integrates the two has been a grand challenge in modern physics, and has confounded many of the greatest minds in the field.
Biochemistry is a reductionist discipline, for example: its modus operandi is the dissection of biological phenomena to yield hypotheses that may be tested. It has furnished us with very precise understanding about the smallest units in biology – molecules. In some cases (for example, the Krebs cycle), the painstaking assembly of sequences of molecular interactions has been possible. However, biomolecules function within cells – large systems of interacting molecules. Even a single biological process may involve a very large number of interactions. For example, the signalling pathway for tissue cell attachment involves some 200 different molecules. A single mechanism such as this stretches the reductionist approach to breaking point. Many cells, of differing types, integrate to form an organ; organs and tissues are integrated in organisms and ecosystems consist of many interacting organisms. At this level biological systems exhibit breathtaking complexity. Indeed, it has been argued that in many important senses biological systems may be irreducibly complex. The recognition of this challenge has led to the birth of systems biology, in which computational approaches are utilised to attempt to model large networks of interacting elements. However, systems approaches remain disconnected from the molecular-scale understanding furnished by biochemistry, the most precise biological knowledge at our disposal.
We believe that the challenge of developing an integrated understanding that spans the length scales – from molecules to systems – is of central importance in biology. We also believe that physicists can contribute much to addressing it; indeed, that the challenge of integrating biological understanding across the length scales is identical with the challenge of understanding the physics of life. A grand unified theory of physics that integrates quantum theory and relativity is elusive. However, in statistical physics, quantum mechanics is integrated into an analysis of the behaviour of ensembles of molecules that has enabled macroscopic properties to be modeled realistically. The application of theoretical physics to the important problems associated with spanning the length scales in biology may yield fruit. Physics has provided experimental methodologies that have facilitated many major breakthroughs in modern biology. The time seems right to try to draw together experimental and theoretical physicists interested in these problems, in partnership with biologists, to form a large community that together can seek an integrated understanding of biological behaviour from molecules to systems.