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.

The penton fibres
consist of a slender shaft with a globular head.
They are involved in the process of attachment of the virus particle to the host cell.

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.

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