Two-state dynamics of single biomolecules in solution

Recent fluorescence decay experiments on an ensemble of chromophores, each tethered to a large DNA molecule, show a biexponential relaxation in time. Experiments on individual molecules also show biexponential relaxation, but with a wide distribution of the relative weights of the two components. This indicates that on the time scale of the single-molecule experiments, the molecules are jumping between two possible states. We show that a stochastic two-state jump model can provide a quantitative description of these experiments. Recent similar experiments on single tRNA molecules are also analyzed with the model.