Biophysics of the Pyrenoid

Phase-separated liquid droplets organize molecules in cells, but the underlying physical principles differ from abiotic mixing and quantitative rules in living systems remain poorly understood. The pyrenoid – a liquid-like organelle that enhances photosynthetic carbon fixation in algae and hornworts – provides an unusually tractable model system. Here, we review recent advances in our understanding of pyrenoids from the perspective of biophysics. We highlight how reaction-diffusion models connect compartment architecture to catalytic performance, how soft matter theories link molecular interactions to condensate assembly, and how modern experimental methods enable these predictions to be tested quantitatively. Recent studies suggest that pyrenoid function may be described by a small number of effective transport and reaction processes, while condensate assembly can be understood through molecular design parameters and thermodynamic constraints. Together, these findings establish the pyrenoid as a powerful system for investigating catalytic compartmentalization, biomolecular self-organization and the emergence of effective physical descriptions in living systems.