Life exists by virtue of collective phenomena. From the cells in a tissue down to the proteins inside a cell, cooperation is key for function and thus survival. We study the physics of these many-component systems, looking for the emergent behaviour that underlies many biological processes. Moreover, we do so while taking the direct environment of our objects of interest into account.
In this talk, I will focus on two example systems, one at the population and one at the protein level. At the population level, many cells form a colony, or a tissue, in which no single cell is designated the `leader’; nonetheless, the individual cells depend on the collective’s behaviour for survival. The global properties of the colony on the other hand ultimately derive from the local interactions between the individual cells. However, as I will show in the talk, the global behaviour will be dictated by two perhaps unexpected factors: the colony size and the number of orientational defects inside the colony. At the protein level, we consider the interactions between membrane-embedded proteins through the curvature deformations they impose on that membrane. At scales found inside actual cells, these membranes are both significantly curved and closed, which strongly affects the interactions. These interactions in turn again lead to pattern formation at the scale of the whole system. Consequently, as I will show here, global features like the constriction rings found in cellular division and the long tubules found for example in neurons can emerge spontaneously.
Although these two examples differ on virtually all details, they illustrate a basic principle underlying life: the combination of local small-scale physics with the global constraints set by the geometry and topology of the system can lead to global, large-scale biology.