Molenaar developed a method which makes it possible to follow the movements of RNA molecules in living cells. The researcher also made the movements and interactions between proteins in living cells visible with the aid of the revolutionary "Green Fluorescent Protein".
Much of the present knowledge about molecular compositions of the cell and the mechanisms in which biomolecules such as DNA, RNA and proteins play a role, is based on experiments in tests tubes with biomolecules isolated from cells. However, with these molecules it is difficult to simulate the behaviour in a living cell. Dynamic processes in the cell can only be understood with living cell microscopy.
Molenaar used fluorescent probes which specifically bind to the molecule he wanted to study. By using a fluorescent microscope to examine where a fluorescent molecule was at different times, the movement of the structures containing these molecules could be followed. For example, the researcher followed the tips of chromosomes (telomeres) in three dimensions over the course of time.
The mobility of populations of molecules was visualised using FRAP (Fluorescence Recovery After Photobleaching). The fluorescent molecules in a small part of the cell are destroyed when a laser is focussed on them. However, although it no longer fluoresces, the biomolecule to which the fluorescent molecule is attached remains intact. The rate at which the fluorescent molecules from the surroundings move into this dark area says something about the mobility of, for example, a certain type of RNA or protein. This mobility in turns provides further information about the functioning of the molecules.