Kinetoplast and flagellum of a Leishmania promastigote cell. The image shows a longitudinal section through the anterior end of the cell, where the flagellum emerges from the flagellar pocket. The basal body of the flagellum is connected at its proximal end to the mitochondrial membranes and the kinetoplast. The kinetoplast contains the mitochondrial DNA (kDNA), organised in a network of circular DNA molecules, which forms a compact disk-shaped nucleoid that is visible in this section as an electron dense bar-shaped structure. Leishmania mexicana promastigote forms (WHO strain MNYC/BZ/62/M379) were grown in M199 culture medium. Cells were fixed with glutaraldehyde, post-fixed with osmium tetroxide, dehydrated in ethanol and embedded in epoxy resin. Thin sections (~90 nm) were viewed on a Philips Technai 12 transmission electron microscope operating at 80 kV. magnification 23000.