Which term describes a polyhedral shape commonly found in viral capsids?

• A. Helical
• B. Icosahedral
• C. Enveloped
• D. Polyhedral

Answer: (D)

In virology, capsid geometry is described by the symmetry of the protein shell that encloses the genome. Many viruses use a highly symmetric polyhedral shell because it provides a sturdy, efficient way to package genetic material with identical building blocks.

The term that best describes this commonly used polyhedral shape is icosahedral. An icosahedral capsid has 20 triangular faces and high symmetry, which allows identical subunits to assemble into a closed, robust shell with relatively few different components. This makes icosahedral geometry the standard way to describe that specific polyhedral form.

The other options don’t name this precise geometry: a helical capsid refers to a rod-like spiral arrangement, an enveloped virus has a lipid membrane surrounding the capsid, and polyhedral is a broad descriptor that isn’t specific to the common icosahedral shape.