A protein-synthesis organelle called the endoplasmic reticulum is shaped like a spiralling car park — and can add new levels as needed.

A team led by Mark Terasaki at the University of Connecticut Health Center in Farmington and Tom Rapoport at Harvard Medical School in Boston, Massachusetts, produced extremely detailed electron microscopy images of the organelle by staining very thin sections using a technique that accentuates the membrane sheets from which it is built. This method revealed sheets that form a twisting, continuous membrane with layers connected by helical ramps. The team described this geometry precisely using mathematical modelling and showed that the structure allows for dense, adjustable packing of material in the cell, boosting the surface available for protein production within a small volume.

Cell 154, 285–296 (2013)