The ability of DNA to self-assemble into one-, two- and three-dimensional nanostructures"', combined with the precision that is now possible when positioning nanoparticles(5-19) or proteins(20-24) on DNA scaffolds, provide a promising approach for the self-organization of composite nanostructures(25-27). Predicting and controlling the functions that emerge in self-organized biomolecular nanostructures is a major challenge in systems biology, and although a number of innovative examples have been reported(28-30), the emergent properties of systems in which enzymes are coupled together have not been fully explored. Here, we report the self-assembly of a DNA scaffold made of DNA strips that include 'hinges' to which biomolecules can be tethered. We attach either two enzymes or a cofactor-enzyme pair to the scaffold, and show that enzyme cascades or cofactor-mediated biocatalysis can proceed effectively; similar processes are not observed in diffusion-controlled homogeneous mixtures of the same components. Furthermore, because the relative position of the two enzymes or the cofactor-enzyme pair is determined by the topology of the DNA scaffold, it is possible to control the reactivity of the system through the design of the individual DNA strips. This method could lead to the self-organization of complex multi-enzyme cascades.