“There are no wires” - The mechanism of cellular computation is diffusion and genetic code
Since Thermal diffusion is the mediator for cellular computation, computation happens through the continuous high-intensity bumping of proteins into each other, and is determined by base pair sequences encoded in DNA. Diffusion introduces ample noise into genetic outcomes.
Not all computation happens “in the wet” and through random collisions, though: Cellular processes work with “addresses” through microtubules and transport molecules.
References:
Bray, Wetware (2009), p. 87
It is a very different kind of computational machine from those we are familiar with, and it takes some getting used to. There are parallels between the action of individual protein molecules and that of the components of an electronic circuit. But there are also huge differences. A protein molecule is perhaps a thousand times smaller in linear dimension than a silicon transistor. As though in compensation, however, it is usually present in thousands of individual copies, scattered in different locations in a single cell. Many molecules, especially the small ones, are in continual violent motion owing to thermal energy. How can you connect circuits under these conditions? Where are the wires?
The answer is that the wire-equivalents are molecules that diffuse and interact. Typically, a molecule made by one enzyme diffuses a short distance to the second enzyme. En route, it makes fleeting contact with thousands of other molecules. But it disregards these encounters and comes to rest only when it reaches the second enzyme. Only this protein has a binding site that matches the contours of the diffusing molecule so tightly that it binds and sticks. The first enzyme has now influenced the second, not through the passage of electrons in a copper wire but by the physical movement of a molecule.
p. 88
We might also compare how connections are made. In an electronic device such as a television, functional units of different sizes are connected by a highly logical arrangement of electrically conducting links. In comparison, the wiring of a cell rests ultimately on the atomic structures of its large molecules. Their structures specify the molecules they will interact with and what effect this will have whether, for example, a protein will be modified by addition of a phosphate, and where (at which amino acid).
Ultimately, the wiring diagram-or, more accurately, the recipe for making the connections-is written in the sequences of base pairs in DNA, since these specify the three-dimensional shape and surface chemistry of proteins. But the actual formation of connections themselves is left to the haphazard process of thermal motion. It's as though a collection of electrical components-resistors, transistors, capacitors-had been labeled with individual numbers, put into a bag, shaken so that their positions were randomized, and then connected according to their numbers. This would be a nonsensical task for an electronics engineer: for one thing, there would not be enough space for all the wires. But for a living cell full of freely diffusing molecules, it is a highly practical solution.