ABSTRACT
Up to now we restricted ourselves to the discussion of systems in
equilibrium for which the framework of Chapter 2 can be applied.
However, many processes in the cell are non-equilibrium processes.
Consider, for instance, the processes that take place within the
central dogma of molecular biology, Fig. 1.1. Transcription and
translation are both processes where a machine walks along a
biopolymer (DNA or RNA) and reads out the sequence of bases in
order to polymerize another biomolecule (RNA or protein). This is
certainly not an equilibrium process that happens spontaneously
without external input. In fact, like machines in our daily life,
polymerases and ribosomes consume energy in order to perform
their jobs. Another process that takes place in Fig. 1.1 is the folding
of a protein. The process of going from an unfolded configuration
to a unique collapsed state does not require external energy input
but it is nevertheless not an equilibrium process: the unfolded state
is energetically unfavorable and the folded state is energetically
favorable. So protein folding has to be understood somewhat similar
to the downhill flow of water in a mountainous landscape. In
fact, one might go so far and say that maintaining cells in a non-
equilibrium state is right at the heart of being alive.
