In a mirror dimly: tracing the movements of molecules in living cells

The random movement of molecules (diffusion) is fundamental to most cellular processes, including enzymatic reactions, signalling, protein-protein interaction, as well as domain and pattern formation. Despite playing a central role, diffusion is, to a large extent, under-appreciated in the cell biology community. One reason for this is that diffusion is rather challenging to study in living cells. This article is intended to explain, at least in part, how we can go about studying diffusion of molecules in living cells, why it is important and how it provides us with important clues about biological systems. As the title 'In a mirror dimly' suggests, we do this by monitoring faint light emitted by fluorescent probes or proteins using advanced optics (e.g. mirrors) and electronics. The data are then fitted and interpreted with mathematical and physical models, providing a glimpse into the world of molecules.