Computer molecular graphics of an adenovirus, cause of infection to the upper respiratory tract, the symptoms of which resemble a common cold. The virus contains DNA surrounded by a protein capsid, or coat (seen here), which is composed of 252 capsomeres (hexagonal subunits) arranged into an icosahedron, or 20-faced figure. The 12 capsomeres surrounded by only 5 neighbours are called pentons (pale blue hexagons). They consist of a base & a stick-like projection. The remaining capsomeres with 6 neighbours are called hexons.