ABOVE: © KIMBERLY BATTISTA
Alongside organelles such as mitochondria and Golgi apparatuses, membraneless structures help compartmentalize the cytoplasm, as well as the interior of the nucleus. In contrast to organelles with a lipid bilayer membrane, membraneless structures are formed through a process known as liquid-liquid phase separation. When it comes to how and why cells create and use membraneless organelles, however, there are still more questions than answers.
For liquid-liquid phase separation to occur in cells, the polymers that make up membraneless organelles—typically highly flexible proteins and nucleic acids—must exceed what is called their saturation concentration, or ”solubility limit,” in the cytoplasm or nucleoplasm. Below this level, the polymer chains dissolve into the surrounding cellular solution; if the saturation concentration is exceeded, the extra polymer chains condense into liquid-like droplets. The polymer chains inside and outside the droplets are therefore in equilibrium, meaning they continuously escape and rejoin the membraneless ...
