Agenda

Speaker: Roberto Serra, Modena and Reggio Emilia University

Abstract

While present day cells are endowed with highly sophisticated mechanisms, which represent the outcome of billion years of evolution, it is widely believed that the first life-forms were much simpler. Such protocells should have an embodiment structure, a simplified metabolism and a way to give rise to new protocells that are similar but not necessarily identical to their parents. Besides their relationship to the origin of life, protocells may be of much practical interest: it is indeed possible to envisage populations of such entities which grow and reproduce, that are selected to perform useful tasks like e.g. drug synthesis.
 It is important to understand under which conditions these systems can actually evolve and models are required to address this issue. Several different protocell "architectures" have been suggested but, notwithstanding the heterogeneity of the various proposals, it has been shown that at least one of the major problems in protocell modelling can be dealt with in a unified way. This is the problem of synchronization between the rate of duplication of the lipid container and that of the genetic material (obviously a necessary condition for the sustained growth of a population of protocells). In the first part of the talk I will review results that show that such synchronization emerges spontaneously, generation after generation, under a broad set of different hypotheses. It has been shown that even chaotic replicator dynamics can give rise to such synchronization in protocells.
 Another major question concerns the products of a large web of interacting chemical substances: several abstract models, which differ in many respects, suggest that large collectively autocatalytic sets of molecules should appear, provided that the number of different chemical species exceeds a certain threshold. On the other hand, news from the lab are not so good, so one should try to understand where the difference can come from. Indeed, the "optimistic" theoretical results have been mostly obtained by using graph-theoretical arguments, and I will discuss how the outcomes can be affected when the dynamics is taken into account. In order to do so, it is necessary to resort to a truly stochastic approach, since new molecular types that appear at a certain time are usually present at very low concentrations. Moreover, while the models that take dynamics into account are usually based on open-flow reactors, it can be shown that the hypothesized protocell behaves in a very different way. We have recently introduced a model of a semipermeable protocell and I will discuss the main results of its application to protocell dynamics, including the conditions for synchronization and the notion of a RAF set. Some interesting phenomena will be described and some reasons why it may be hard to get a working protocell will be highlighted. These observation might provide suggestions for new experiments.