Question

What benefits might the cell gain by organizing molecules into phase-separated bodies as opposed to membrane-encapsulated bodies like organelles?  

Answer 1

Cell essentially needs compartmentalization for ‘division of labor’ and harmony in the cell. Membrane bound organelles include mitochondria, lysosomes etc. Membrane less organelles include nucleoli, Cajal bodies in nucleus and centrosome in cytoplasm. These membrane-less entities don’t expose and mix their contents in the cytosol. However, their contents are maintained by a process called phase separation. Such entities have the characteristics of organelles which help them compartmentalize which includes, optimum concentration of reactants for metabolic reactions, phagocytosis of harmful particles, storage of food reserves and cell signaling. Cytoskeleton are concentrated by phase separation which helps nucleate filaments for these membrane-less organelles. Such entities have protein aggregates which hints at a rescue mechanism for the cell to keep away toxic molecules. They function as storage granules especially during stress conditions. Also they concentrate receptors and signaling molecules, which will help amplify signaling pathways. More complex advantages of membrane-less systems over organelles requires further research. I would like to acknowledge this reference for lot of current research content on this topic: ‘protein phase separation: a new phase in cell biology, Trend Cell Biol. 28(6), 2018’.