1. Introduction to Virus Structure and Diversity
By: Dr. Laxmi Kant Pandey

2. What is Virus…?
A virus is a biological agent of microscopic size that reproduce inside the cells of living host (humans, animals, plants, bacteria).

3. Virus Structure Size Basic shape Genomic material Capsid
17 nm – 3000 nm diameter
Basic shape
Rod-like
Spherical
It has mainly two components
A nucleic acid genome and a protein capsid that covers the genome
Genomic material
DNA or RNA
Single- or double-stranded
Capsid
Made of many identical protein subunits
Symmetrically organized
Enveloped or non-enveloped

5. Electron Micrograph of HIV virus

6. Virus Structure Virus capsids function in:
Packaging and protecting nucleic acid
Host cell recognition
Protein on coat or envelope “feels” or “recognizes” host cell receptors
Genomic material delivery
Enveloped: cell fusion event
Non-enveloped: more complex strategies & specialized structures

8. Icosahedral Symmetry 12 vertices 20 faces 5-3-2 symmetry axes
(equilateral triangles)
5-3-2 symmetry axes
60 identical* subunits
in identical environments
can form icosahedral shell
* asymmetric

9. Baltimore classification of Virus
Baltimore classify viruses in to 7 groups
It is based on-
Nucleic acid (DNA or RNA)
Strandedness (ss or ds)
Sense (positive or negative)
Method of replication

11. Group
Name of the virus I
Adenoviruses, Herpesviruses, pox viruses II
Parvo viruses
III
reoviruses IV
Picornaviruses, togaviruses V
Rhabdoviruses VI
Retroviruses
VII
Hepadnaviruses