Adenoviruses. Coloured transmission electron micrograph (TEM) of three adenovirus particles, cause of respiratory tract infections in humans. There are many members of the adenovirus family. Each virus is composed of an icosahedral (20- sided) protein shell, or capsid (angular orange spheres), which encloses the genetic material, deoxyribonucleic acid (DNA). Interaction with a target cell is mediated by glycoprotein fibres that protrude from the capsid surface. Respiratory tract infection results in symptoms similar to those of the common cold. Infections of the eyes and gut also occur. Magnification: x62,500 at 6x6cm size.