For example, PSI is investigating the structure of filamentous structures, the so-called microtubules, which, among other things, pull apart chromosomes during cell division. They consist of long protein chains. When chemotherapy is used to treat cancer, it disturbs the assembly or breakdown of these chains so that the cancer cells can no longer divide. Researchers are closely observing the structure of these proteins and how they change to find out exactly where cancer drugs have to attack the microtubules. With the help of PSI’s SwissFEL free-electron X-ray laser, which was inaugurated in 2016, researchers have been able to analyse dynamic processes in biomolecules with extremely high time resolution – less than a trillionth of a second (picosecond). For example, they have detected how certain proteins in the photoreceptors of the retina of our eyes are activated by light.