Noise in Biological Systems


Noise is generally defined as unnecessary elements that may arise during the course of generation or transmission of signals. Noise may be big or small, significant or insignificant, with or without any pattern, but one characteristic that remains constant is that it is unwanted. How do we define noise in biological systems, if there is any? How detrimental is it to our understanding of these systems? I will try to highlight these in this post, amidst  a lot of noise in my head over the recent weeks.

Signal and noise – the inseparable duo

The very basic signal in biological systems is the state of the gene. It can be either switched on or off. But, the scenario seems more binary than it actually is. Two genetically identical cells with a particular gene switched on do not make equal amounts of proteins. Proteins are the secondary level of the signals in biological systems. Their concentrations have also been compared to binary units, high denoting 1 and low denoting 0. But again, the high’s of two genetically identical cells differ considerably. Genes, proteins and hence the noise associated are communication relayed not just across space (inter-cellular or inter-individual), but also across time by guiding evolution. Just as we come up with ways to minimize noise in our communication systems, we would expect nature to minimize noise in its systems too. Observers, in their obvious hate for biological noise, termed the deviations of the individual from the average as errors due to the limits of measurement.

Is noise really that bad?

Now with methods to analyze individual cells, we come to a counter-intuitive explanation. The noise is not a slight deviation from one of the two bi-stable states, but the decisive factor behind which of the two states exists under the given conditions and is shaped by evolution. The paper below explains the sources of noise in gene expression, its adaptive role and evolutionary importance.

Read more here

Viney, M., Reece, S. E., Adaptive noise, Proc Biol Sci. 2013 Jul 31

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