Mitochondrial deoxyribonucleic acid (mtDNA) plays a key role in the regulation of cell growth and survival. It has been demonstrated that mutations in mtDNA have an impact on survival for cancer patients, and studying these alterations may therefore provide valuable insight into cancer progression and tumorigenesis.  In this project, three mtDNA genes, MT-COX3, MT-CYB and MT-ATP6 have been knockout out from Human Embryonic Kidney 293T (HEK293T) cell models to investigate their role in tumorigenesis and cancer progression. Knockout cell models developed for MT-COX3 and MTATP6 was successful obtained, however no satisfactory knockout cell model for MT-CYB was obtained, limiting the investigation to MT-ATP6 and MT-COX3. The function of these two genes were investigated using numerous techniques including measuring cell growth, cell metabolism, and mitochondrial function. The results suggests that the knockout of the genes reduces the proliferation and viability of the cells. It also causes the cells to shift their metabolism and reduces mitochondrial function in general. This suggests that both MT-ATP6 and MT-COX3 are important for proper function of the investigated cells. Based on the findings, it can be concluded that mitochondria play an important role for the fitness of the investigated cells and that mtDNA may be a potential target for cancer treatment.