ABSTRACT
In this chapter, I describe different ways in which flipons can enable logic gates, following traditional concepts based on Boolean logic. I give simple examples based on RNA splicing and switches formed by variations in flipon conformation.
Current approaches for engineering such circuits into cells are based on the current schemes used in computer circuits. The logic is transitive, with A leading to B, then to C. The designs add to our existing understanding of cell biology, but there are limits to the number of such logic gates that can be built into a cell.
Despite this limitation, the approaches are currently of much interest. Biocircuits to measure the therapeutic response to drugs or to regulate bioengineered cell therapeutics are on their way to the clinic. For example, the engineered cells can control delivery of therapeutics such as insulin when blood glucose levels rise but then stop delivery when the glucose concentrations fall below a particular level. For many applications, the desired circuits could be evolved in cells to optimize performance, reducing the cost of their development. Such devices, once implemented, are cheap to make. The cells can be fabricated on a large scale in a bioreactor, reducing the cost of manufacture. Furthermore, the devices are inherently self-repairing using the fixit pathways that Nature has evolved over the eons.
The chapter lays the groundwork for the following chapter on how intransitive logic is implemented in a cell and how that too is evolvable. With this logic, A leads to B, B to C but then C leads to A. The result is a directed cycle in which there are at least two paths connecting each node, one acting as an input and the other as an output.
