1. Structure and diversity of Virus
Mrs.Praveen Garg
VITS College, Satna

2. Introduction
• A virus is made up of a DNA or RNA genome inside a protein
shell called a capsid.
• Some viruses have an external membrane envelope.
• Viruses are very diverse.
• They come in different shapes and structures, have different
kinds of genomes, and infect different hosts.
• RNA or DNA act as genetic material.
• The nucleic acid may be single- or double-stranded.
• The entire infectious virus particle, called a virion, consists of
the nucleic acid and an outer shell of protein.

3. • The simplest viruses contain only enough RNA or DNA to
encode for proteins.
• Viruses is the link between living and non living.
• Viruses are not considered living because they can't reproduce
by themselves (without a host).
• Viruses have no cells, it is just packages of nucleic acid and
protein.
• A virus is a submicroscopic infectious agent that replicates
only inside the living cells of an organism.
• Viruses infect all types of life forms, from animals and plants
to microorganisms, including bacteria and archaea.

4. History
• Dutch microbiologist Martinus W. Beijerinck, who coined the
term "virus“.
• Beijerinck is often called the Father of Virology.
• In 1892, Dmitri Ivanovsky discovered the virus firstly in
tobacco plant.
• Tobacco Mosaic Virus is the first virus discovered by
Ivanovsky.

5. Characters of Virus
• They can mutate.
• They are acellular, that is, they contain no cytoplasm or
cellular organelles.
• They carry out no metabolism on their own and must replicate
using the host cell's metabolic machinery.
• In other words, viruses don't grow and divide without host.
• The vast majority of viruses possess either DNA or RNA but
not both.

6. • All viruses contain the following two components:
 A nucleic acid genome or viral core
 A protein capsid that covers the genome. This is called
the nucleocapsid.
• Sometime third component also present.
 Lipid and polysaccharide envelope.
Structure of Virus

8. Viral core:
 It is the nucleic acid component, which makes up the genome
of the virus.
 The viral core provides genetic information that
determines pathogenicity, antigenicity, proliferation, heredity,
variation, etc.
 The chemical components of the viral core are DNA or RNA,
based on whether the virus is classified as a DNA virus or an
RNA virus.
 Nucleic acid can be single or double stranded.

9. Viral capsid:
 It is a protein shell that surrounds and protects the nucleic
acid from digestion by enzymes.
 It contains special sites on its surface that allow the virion
attach to a host cells.
 One of the viral structural proteins (either an
envelope glycoprotein for the enveloped viruses or a capsid
protein for the nonenveloped viruses) directly binds to the
cellular receptor, for the viral entry.
 The viral capsid is composed of repeated protein subunits
known as capsomere.
 It enable the virion to penetrate the host cell membrane and,
in some cases, to inject the infectious nucleic acid particles.

10. Envelope:
• Envelope is the one or two layers of membrane that surround
the capsid of some viruses.
• The envelope is formed during the maturation process when
certain viruses bud out from the cell membrane.
• Therefore, the envelope can be composed of the host cell
membrane and/or the nuclear membrane.
• The surface of some viral envelopes carries protein
protrusions called peplomers or spikes.

11. Classification
Viruses are classified into
four groups based on
shape:
 Filamentous,
 Isometric (or icosahedral),
 Enveloped, and
 Head and tail.
• Many viruses attach to
their host cells to facilitate
penetration of the cell
membrane, allowing their
replication inside the cell.

12. The diversity of Viruses
• Viruses show great diversity in their genome structure and
replication mode.
• Viruses have been found that attack animal cells, plant cells,
and bacterial cells.
• Different viruses have from three to just over 2500 genes.
• Many viruses replicate their genomes by some form of rolling
circle mechanism with the RNA replicase enzyme.
• Virus particles come in a wide range of sizes and shapes.
• Bacteriophage is a common virus have an larger genome.
• Bacteriophage ΦX174 is a small simple spherical virus that
contains 5386 bases of circular single-stranded DNA.
• Bacteriophage M13 is a filamentous shape. It has single-
stranded circular DNA.

13. • Complex Bacterial Viruses With Double-Stranded DNA that
infects B. megaterium.
• There is a large family of bacterial viruses that all have a
complex form made up of a head, tail, and tail fibers.
• This group includes some of the most complex known viruses.
• The head of the virus particle contains a large molecule of linear
double-stranded DNA.
• They include bacteriophages T4, Lambda, P1, and Mu, which are
all used in bacterial genetics.

15. Thank You