This bachelor's thesis deals with changes in mitochondrial metabolism in tumor cells. The introductory part focuses on the morphology and functions of mitochondria. The main part of the thesis deals with the features of tumor cells. The remaining part explains the changes in their mitochondrial metabolism with a special focus on the role of the succinate dehydrogenase enzyme. Part of the work is also dedicated to mitochondrial biomarkers used for diagnostics and therapy of mitochondrial diseases.