HeLa cells, confocal light micrograph. The cell nuclei, which contain the cells' genetic information, are blue. Mitochondria, a type of organelle, are red. Mitochondria oxidise sugars and fats to produce energy in a process called respiration. HeLa cells are a continuously cultured cell line of human cancer cells. They are immortal and so thrive in the laboratory. HeLa cells are widely used in biological and medical research.