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Are there any famous biological processes that depend strongly on a chemical concentration reaching a particular value, like some sort of switch?

E.g. if concentration of chemical x reaches concentration y at cell location z (membrane, organelle etc) then a particular biological process will occur?

Thanks

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There are several, but I guess the most well known is the neuron action potential, where the concentrations of Na+, K+, and Cl- ions determine the membrane potential of the cell. When the potential reaches a certain level, it triggers the action potential. You can read about this in much more detail on wikipedia, https://en.wikipedia.org/wiki/Action_potential .

But to be pedantic about it, almost every cellular process is concentration dependent.

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  • $\begingroup$ thanks that helps. I was also thinking along the lines of "everytime a cut off value is reached, this physiological process occurs" something like cell death, or signalling or repair.... $\endgroup$ – RNs_Ghost Aug 11 '14 at 23:36
  • $\begingroup$ "But to be pedantic about it, almost every cellular process is concentration dependent." Do you think that I could find a proper source on that, like a review paper or something - I need to be able to justify this to my supervisor! $\endgroup$ – RNs_Ghost Aug 12 '14 at 9:33
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What you are basically asking is if there are cellular processes that are thresholded (ultrasensitive). Yes; there are many examples and it would be difficult to list them all.

There are different mechanisms by which such a switch like behaviour can be implemented. Positive feedback loops and co-operativity (in transcription factor binding or enzyme-ligand binding) are common mechanisms by which such switches can be implemented. Have a look at this wikipedia page. For more details you can refer to a book on enzyme kinetics and non-linear dynamics. If you search co-operativity and postitive feedback loops then you will find studies on specific examples.

But as already pointed in the other answer, almost all cellular processes are concentration dependent. There are a very few examples where you can actually observe zero order kinetics.

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