  A central goal of synthetic biology is to design sophisticated synthetic
cellular circuits that can perform complex computations and information
processing tasks in response to specific inputs. The tremendous advances in our
ability to understand and manipulate cellular information processing networks
raises several fundamental physics questions: How do the molecular components
of cellular circuits exploit energy consumption to improve information
processing? Can one utilize ideas from thermodynamics to improve the design of
synthetic cellular circuits and modules? Here, we summarize recent theoretical
work addressing these questions. Energy consumption in cellular circuits serves
five basic purposes: (1) increasing specificity, (2) manipulating dynamics, (3)
reducing variability, (4) amplifying signal, and (5) erasing memory. We
demonstrate these ideas using several simple examples and discuss the
implications of these theoretical ideas for the emerging field of synthetic
biology. We conclude by discussing how it may be possible to overcome these
limitations using "post-translational" synthetic biology that exploits
reversible protein modification.
