How hard is it to encapsulate life? The general constraints on encapsulation.

Many studies of the origins of life focus on the advantages of encapsulation. Independent of these advantages, there may be serious challenges to overcome for a system to become encapsulated. Here, we address the general constraints associated with encapsulating a biotic system. We first consider the extant biochemical system of Earth and show that small changes in the rates and sizes of macromolecules can easily make encapsulation difficult. We show that if the ribosome is slower for its size, there is a threshold where modern life could not be encapsulated in cells. We also show how the largest cells are limited by the ribosome rate per size. We are not committed to this system as being universal, but it provides a nice test case where we have complete knowledge of the dynamics and molecular features. To generalize our results, we considered a generic autocatalytic system and a system that has separated informational and functional molecules. In both cases, we find bounds on the allowable growth rates of cells based on the effective rates and volume fractions of cells. We also illustrate how environmental loss rates set the allowable volume fraction of cells as a function of the effective catalytic rate of an autocatalytic set. These results provide a general window into the challenges of encapsulation for any prebiotic or biotic system and are applicable in diverse contexts from the origins of life, to astrobiology, to synthetic biology.This article is part of the theme issue 'Origins of life: the possible and the actual'.