What does an icosahedral capsid consist of?

Explanation

An icosahedral shape, common in viral capsids, is made of protein subunits called capsomeres, which can be pentameric (five subunits) or hexameric (six subunits). Pentamers occupy the 12 vertices of the icosahedron, while hexamers fill the faces and edges, creating a stable, closed shell. This arrangement follows the principle of quasi-equivalence, allowing subunits to adapt slightly to form either pentamers or hexamers. The combination of these capsomeres gives the icosahedral capsid structural stability and enough internal space to enclose the viral genome.