Virus structure. Animation of proteins aggregating to form the external structure of a virus particle (virion). Atoms are represented as spheres. Viruses are microbes that consist of a nucleic acid core (DNA or RNA) surrounded by a protein shell (capsid). A common shape for virus particles is the icosahedron shown here. This regular polygon has 20 faces (triangles). It has 30 edges and 12 vertices. Examples of viruses with an icosahedral structure include the herpes virus.