Fluctuations for good and bad: The role of noise in living systems

The intention is to provide a broad overview of the role of noise and basic methods to describe noise effects in biological systems. It starts from a brief discussion of the statistical mechanical basis, and Brownian motion which is generalised to calculations of randomly induced transitions over energy barriers, and stochastic resonance. The description of discrete step processes provides another approach, which also is a basis of a stochastic description of chemical reactions. Macromolecular structure changes are considered as triggered by the background fluctuations. A strong emphasis is put on “fluctuation–dissipation” relations, relations between the irregular fluctuations and the dissipative spreading of energy towards a most probable distribution. We also take up some applications to non-linear systems, noise effects together with oscillations and signal transmission as well as models on unidirectional motion of various kinds with Brownian ratchets and active transport as examples.