In a living organism, numerous inanimate biomolecules and their inherently stochastic interactions are precisely orchestrated and organized in space and time, together enabling the enigma of life. By using single molecule fluorescence microscopy we obtain an exceptionally detailed view on life processes in the natural environment of a live cell or embryo. Tracking individual molecules yields quantitative information such as reaction rate constants, diffusion coefficients and the spatial distribution and stoichiometry of cellular structures. Thus, we obtain information necessary for a deep understanding and modeling of life processes. 

I will give a short overview over our imaging methodologies and then focus on recent findings regarding the dynamic cell-cycle dependent action of chromatin-structuring proteins and the implications of transcription factor - DNA  interaction kinetics on the transcription process and on the activation of transcription in zebrafish development.