Adenovirus particles. Coloured transmission electron micrograph (TEM) of a section through adenovirus particles (virions, round). Adenovirus particles (virions) are composed of a protein coat (capsid) encasing DNA (deoxyribonucleic acid), the genetic material of the virus. They cause a wide range of diseases, from respiratory infections such as the common cold, to conjunctivitis (eye infections) or gastroenteritis (digestive tract infections). Magnification: x105,000, when printed 10 cm wide.