Mitochondria are responsible for generating most of the energy in cells and can be thought of as cell powerhouses. They contain their own genomes containing 37 genes, and mutations in these genes can result in a wide range of human diseases. However, understanding the involvement of mitochondrial gene mutations in disease is difficult because there are currently no tools available to manipulate mitochondrial DNA in cells. Our aim is to develop technology that will enable the replacement of mitochondrial genomes in cells with custom-designed synthetic genomes. We will collaborate with the J Craig Venter Institute (USA) to build synthetic mitochondrial genomes that contain traceable markers. The synthetic genomes will be transported into the mitochondria of cells using a specially designed protein that can bind DNA and traffic it directly into mitochondria. If successful, our research will revolutionise mitochondrial genetics and will advance understanding of the involvement of mitochondria in disease.