I have a thing about noise (see my ramblings here). And as folks try to turn elements of biological circuits into well-behaving engineered parts, I’ve been trying to put my finger on why biological noise means so much to me.
A series of articles in Nature back in September covered the cost of feedback control, the fundamental limits on the suppression of molecular fluctuations, the functional roles for noise in genetic circuits (subscription required for all three).
The main review mentions that noise is a nuisance in the design of deterministic (engineered) circuits. But goes on to show that noise in biological systems provides critical functions that are hard to achieve with deterministic circuits.
Noise in biological systems is unavoidable, there are limits to how much a feedback system can reduce noise. And the review goes on to discuss many areas where noise is integral to the stability or responsiveness of a process, such as gene expression coordination, state-switching, positive feedback, differentiation, and in development.
How might we understand this noise and actually engineer it into our deterministic circuits?
One thing, though, that tempers my bias towards keeping noise in biologically engineered circuits is that digital electronics also had their start in a noisy analog world. Will engineering biological circuits be forever mired in the analog noisy world of biology or will these circuits eventually be complex enough to exhibit the precise nature that biological engineers seem to want? Should biological engineers seek to incorporate noise into their calculations or strive to limit stochastic fluctuations?
Really, that’s a bit beyond my ability to understand circuit design and noise and all, so I leave it to smarter folk than I. :-)
Image from BarelyFitz