Here we combine the principles of DNA nanotechnology with synthetic biology to solve a number of problems facing researchers in material science, biology, and medicine. We constructed well-defined multi-dimensional RNA assemblies inside cells, and used them to scaffold the enzymatic machinery responsible for hydrogen production. We improved hydrogen biosynthesis 48 fold. We also built DNA/protein assemblies ex vivo, and used them to scaffold cell adhesion and growth. The DNA was used to modulate scaffold stiffness, and to control cell morphology, behavior, signaling, and transcription factor localization. Overall, this work provides a set of simple solutions to some of the bigger problems facing researchers in metabolic engineering and tissue engineering, and offers a snapshot of what is to be expected from the symbiosis that is synthetic biology and DNA nanotechnology.