Adenoviruses are non-enveloped icosahedral particles.
The capsid is built up from 252 capsomers (T=25), of which 240 are hexavalent and 12 (situated at the apices) are pentavalent.
A "penton fibre"projects from each apex.
Fibres easily become detached during preparation for electron microscopy.
Adenoviruses that infect humans are usually mild pathogens, and can cause respiratory illness or conjunctivitis (so-called "pink eye"), but under laboratory conditions some human strains can transform cells in culture.