  Molecular machines transduce free energy between different forms throughout
all living organisms. While truly machines in their own right, unlike their
macroscopic counterparts molecular machines are characterized by stochastic
fluctuations, overdamped dynamics, and soft components, and operate far from
thermodynamic equilibrium. In addition, information is a relevant free-energy
resource for molecular machines, leading to new modes of operation for
nanoscale engines. Towards the objective of engineering synthetic nanomachines,
an important goal is to understand how molecular machines transduce free energy
to perform their functions in biological systems. In this review we discuss the
nonequilibrium thermodynamics of free-energy transduction within molecular
machines, with a focus on quantifying energy and information flows between
their components. We review results from theory, modeling, and inference from
experiments that shed light on the internal thermodynamics of molecular
machines, and ultimately explore what we can learn from considering these
interactions.
