The Long and Short of Templated Copying

Templated copying is the central operation by which biology produces complex molecules. Cells copy sequence information from DNA to RNA and into proteins, which are the molecules responsible for the function and regulation of cellular systems. In the templated copying process the template catalyses the formation of a second molecule carrying the same sequence. Traditionally, people have ignored the separation of the template and copy at the end of the process, but separation is both necessary and fundamentally changes the thermodynamics of the process.

In general, creating an accurate polymer costs free energy. Omitting separation, this can be compensated for by the extra free energy released by “correct” copy/template bonds. Separation requires these bonds be broken, so true copying requires an input of free energy. Copying is a far from equilibrium process. This talk explores the consequences of this observation. We start in the infinite length limit where the costs of accuracy represent hard thermodynamic bounds and then moves to the finite length limit where these same limits can be understood as kinetic barriers. We then discuss copying systems as non-equilibrium steady states, which can be analysed as information engines moving free energy between out of equilibrium baths.