The proper functioning of living cells is brought about by a bewildering number of interconnected interaction processes between very many different molecules and structures.
Each of these processes is governed by the laws of physics and chemistry. However, their sheer number and immense interconnectedness renders it very difficult to identify unquestionable cause and effect relations in living cells. Quantitative analyses of individual processes are even more difficult to achieve. Using well defined model systems is a successful strategy to overcome these obstacles.