The process of cell division requires precise duplication of the genetic material. The separation of the two strands of DNA and the progression of the replisome are driven by replicative helicases called Mini-chromosome maintenance (MCM) proteins. MCMs unwind genomic dsDNA to expose ssDNA template during the S-phase of the cell cycle. We have recently solved the first full-length octameric structure of the Pyrococcus abyssi MCM (PabMCM) by electron microscopy and SAXS. PabMCM can be found as single or double octameric ring assemblies in absence of DNA; however, bound to dsDNA, PabMCM is found exclusively in single ring assemblies bound to the DNA substrate. We now plan to use small angle neutron scattering to solve the structure of MCM/DNA complexes with contrast matching experiments. These are unique experiments that allow to discriminate the protein and DNA component in a full complex.