The division of organelles during the cell cycle requires remodelling and constriction of the organelle membrane, and membrane fission. GTPases of the dynamin family have been implicated in the division of mitochondria, plastids and peroxisomes. However, the molecular mechanism and structural aspects of organelle division are poorly understood. In this issue (p. 853), Yukio Fujiki and co-workers use the unicellular red algae Cyanidioschyzon merolae – containing only one peroxisome whose division can be synchronised through light–dark cycles – to isolate the peroxisome-dividing machinery and to study organelle division in detail. The authors show that the GTP-bound form of dynamin-related protein Dnm1 turns over between cytosolic patches and a dynamin-based ring organising centre (DOC) at the dividing machinery, where Dnm1-GTP is hydrolysed. One DOC forms at the peroxisome-dividing machinery and the dynamin-based ring is formed through unidirectional assembly, which depends on the concentration of GTP. The authors further demonstrate the formation of a second DOC at later steps of membrane fission, which enables construction of a 300–500 nm double dynamin-based ring. With the identification of the DOC as being key for membrane division, this work advances the knowledge of the formation and mechanisms of organelle division in Eukaryota.