Chapter 26, Problem S17.1BYB

Summary Introduction

To write:

The general structure of a virus.

Introduction:

Viruses are small, infectious particles which can multiply only inside a host. They are primarily made up of a viral genome surrounded by a protective protein coat.

Explanation of Solution

The general structure of a virus can be best studied in the form of virions. A complete virus with all the components necessary for infection of a host is called a virion. They are acellular and are made up of a nucleic acid core surrounded by a protective protein coat called the capsid and an outer lipoproteinaceous envelop. These enveloped viruses have a set of glycoprotein based knob-like structures or extensions called the peplomers.

A capsid is derived from the proteins coded by the viral genome and it is made up of the repetitive protein subunits called the capsomeres. A capsid exists in various forms like icosahedral, filamentous and head-like. It is also associated with certain glycoproteins. They help in recognition and binding to the host cells.

The viral genome is made up of a nucleocapsid enclosing the genetic material with proteins. These capsid proteins together with the viral nucleic acid are called the nucleocapsid. Majority of the viruses have RNA as the genetic material. Some viruses contain a layer or cluster of proteins between the capsid and the nucleoprotein called the viral tegument or the viral matrix helping in the replication of the virus.

Conclusion

Thus, viruses are highly infectious particle made up of a viral genome surrounded by a protein coat.