Virus Structure

Viruses are infectious obligate intracellular parasites consisting of an RNA or DNA genome in a protective coat. Virus particles cannot increase in size but are assembled from pre-formed components in susceptible host cells. The assembly of virus particles is achieved by the information contained within the components of the particle, a process driven by the rules of symmetry and by the most thermodynamically stable configuration. Once formed, virus particles vary in stability, some being very fragile while others are extremely stable, enabling some viruses to maintain the infectivity of their genome for extended periods of time outside a host cell, a feature required by viruses which are transmitted environmentally rather than directly from host to host. The outer surface of the virus particle must be able to interact with a suitable host cell to enable the process of infection to occur.