What Cells are divided into rooms called organelles, which allow each room to have a specialized function. Some of these organelles do not have an exterior “wall” and are known as “membrane-less organelles”. These organelles spontaneously assemble from the macromolecules of the cell, which allows them to appear when needed only to disappear again later. We will investigate a mechanism by which such organelles form and dissolve in response to the needs of the cell. Why Biological macromolecules such as proteins, RNA and DNA do not only act as individuals. Some of their properties are emergent and only occur on when their numbers cross a certain threshold. A good example of this is formation of membrane-less organelles, which is likely a common mechanism for controlling biochemical processes. Understanding how cells control such organelles is key to understanding the molecular processes of life, but also for understanding a whole new type of disease mechanisms where this assembly is disturbed. How We will use biochemical methods to investigate how a type of enzyme – phosphatases – act inside membrane-less organelles. We will use synthetic organelles where we can control their architecture to allow us to reach general conclusions that apply to many different phosphatases and type of membrane-less organelles.