INTRODUCTION TO VIRUSES AND THEIR STRUCTURE: PETER H. RUSSELL, BVSc, PhD, FRCPath, MRCVS Department of Pathology and Infectious Diseases, The Royal Veterinary College, Royal College Street, London NW1 OTU. Web siteWeb site

Objectives Students should be able to: Summarise virus properties and control. Describe virus structure and enzymes in outline

Introduction to virology

How are virulent virus infections controlled?

To associate a new virus with a disease it must be grown in pure culture and shown to be virulent.

Virus structure

The nucleic acid: Virus particles do not contain messenger RNA, this is in the host cell A virus will contain either an RNA or DNA genome

The capsid protein The capsid proteins protects the nucleic acid. They are arranged into are 3 forms of symmetry, icosahedral, helical and complex.

Icosahedral capsid An icosahedron has 12 vertices with 20 triangular sides, termed facets, like a geophysical dome. It is made of capsomeres, which appear spherical by em..

Helical capsid

Complex capsid

Envelope

Enzymes and regulatory proteins These are virus proteins which are essential to virus replication. Some are present in the virus particle, others are only in the host cell.

Examples of non-structural enzymes found in the infected cell but not the virus :

Summary Viruses require living cells and are therefore infectious but can be contained by hygiene/vaccines. Several hundred particles which look identical are made in each infected cell overnight. Viruses comprise a nucleic acid surrounded by protein. Some have an additional envelope which makes them more fragile.