Organisms employ a variety of signalling systems to sense and react to their environment. Among the most basic, commonly found in bacteria, lower eukaryotes and plants, are the so-called phosphorelays. These systems transfer sensor information (typically from the cellular membrane) very economically through a chain of chemical reactions.
Despite their widespread use and simple architecture, we are still far from a full understanding of the signal-processing capabilities of phosphorelays.

We investigate the question of whether basic chemical kinetics (kinetics of unar yand binary chemical reactions), formulated as a process algebra, is capable of general computation. In particular, we investigate nondeterministic and probabilistic termination problems. The answers to those problems reveal a surprisingly rich picture of what is decidable and undecidable in basic chemistry.
We introduce an algebra for massive concurrent systems, called reversible structures, where terms retain bits of causal dependencies that allow one to reverse computation histories. These bits permit to trace effects of interactions, but not to the point of being able to identify the precise molecule that caused an effect. The algebra and the causal hints match a particular form of DNA computation.