Drug-DNA complexes. Coloured atomic force micrograph (AFM) of plasmids (pink) of DNA (deoxyribonucleic acid) bound to the anti-cancer drug ditercalinium. This drug distorts the shape of DNA, which eventually causes the death of affected cells. Distorted regions are yellow here. Plasmids are loops of DNA found in some bacteria and yeast cells that exist separately from the cells' chromosomal DNA. They are able to replicate and express their genes independently, and are widely used in genetic research and engineering. Atomic force microscopy produces an image by moving a sensitive tip over a surface. Magnification: x75,000 at 6x6cm size.