STRUCTURE OF A VIRUS - Class 11 Biology Online Notes

NCERT Biology Class 11 - Viruses contain nucleic acid—either DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) and protein. The nucleic acid encodes the genetic information which is unique for each virus. The infectious, external covering (core) of a virus is called the virion. The virion capsid has three functions:

(1) Protection of the viral nucleic acid from digestion by certain enzymes (nucleases).

(2) To furnish sites on its surface that help to recognize and attach (adsorb) the virion to receptors on the surface of the host cell, and, in some viruses.

(3) It provides proteins that enable the virion to penetrate through the cell surface membrane inject the infectious nucleic acid into the interior of the host cell.

It contains at least one unique protein which is synthesized by specific genes in the nucleic acid of that virus. In virtually all viruses, at least one of these proteins forms a shell (called a capsid) around the nucleic acid either DNA or RNA. The capsid consists of numerous capsomers, each having a few monomers or structural units. Each structural unit is made up of one or more polypeptide chains. The different arrangement of capsomeres in the capsid determines the shape of a virion. Viruses have three different types of symmetry as explained below:

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