Kapsomerism

Kapsomerism is a term used in biology, specifically in virology, to describe the structural units that make up a viral capsid. A capsid is the protein shell that encloses the genetic material of a virus. Kapsomers are the individual protein subunits, or sometimes oligomers of subunits, that assemble to form the capsid. These kapsomers are not randomly arranged but follow specific symmetry rules, typically forming either icosahedral or helical structures.

In an icosahedral capsid, kapsomers arrange themselves to form a polyhedron with 20 faces. Each face is an equilateral triangle, and the overall structure has 12 vertices and 30 edges. The arrangement of kapsomers in an icosahedral capsid is highly ordered and can create a stable, protective shell for the viral genome.

In a helical capsid, kapsomers are arranged in a spiral or helical pattern around the viral nucleic acid. This results in a rod-shaped or filamentous virus. The specific angle and spacing of the kapsomers determine the length and width of the helical structure.

The assembly of kapsomers into a capsid is a self-assembly process, meaning the protein subunits spontaneously associate to form the complete structure. This process is crucial for viral replication, as it ensures the efficient packaging of the viral genome and protection from the environment. The number and type of kapsomers can vary significantly between different types of viruses, contributing to their diversity and evolutionary relationships.