Dividing HeLa cells. Coloured scanning electron micrograph (SEM) of HeLa cells undergoing cytokinesis (cell division). Cytokinesis occurs after nuclear division (mitosis), which produces two daughter nuclei. The two daughter cells are still connected by a midbody, a transient structure formed from microtubules. HeLa cells are a continuously cultured cell line of human cancer cells, which are immortal and so thrive in the laboratory. These are the control (untreated) cells from an experiment to treat cultured cancer cells with doxorubicin to investigate cell death. Doxorubicin is a type of chemotherapy drug called an anthracycline. It slows or stops the growth of cancer cells in part by blocking an enzyme called topoisomerase 2. All cells need this enzyme to divide and renew. Magnification: x2600 at 10 centimetres wide. Specimen courtesy of Professor Greg Towers, University College London, UK. For a set of images showing the treated cells see C058/5931 to C058/5967.