False-colour transmission electron micrograph of a group of adenoviruses, the causative agents of many respiratory diseases. The viruses are about 80 nanometres in diameter, and do not have the lipoprotein envelope associated with many other virus genera. The genome of the adenovirus is double-stranded and linear DNA. Adenoviruses were first isolated from human adenoidal glands. Magnification: x146,000 at 6x4.5cm size.