This document provides an overview of viruses, describing their properties, morphology, and classification based on nucleic acid and host types. It details the discovery of viruses, the structure of viral components, and their infection mechanisms. The document also includes the Baltimore classification system, which organizes viruses into seven groups based on their genetic material.

1. Viruses – Morphology & Classification
Prepared By : Ratnaparkhi Sanket Sanjay
S.Y.B.Pharm
Guided By : Mrs. S.D.Raysing Ma’am

2. Introduction to Viruses
• What are Viruses ?
 Virus is a Non-Cellular particle made up of genetic
material and protein that can invade living cells.
 Viruses do not posses cellular organization and they
do not fall strictly into the category of Unicellular
Organisms.

3. Discovery of Viruses
• Dimitri Iwanowski :
 In 1892, He demonstrated that the cause of
tobacco mosaic disease was found in the liquid
extracted from infected plants.
 Discovered of the tobacco mosaic disease.
• Beijerinck :
 In 1897, He suggested that tiny particles in the
juice caused the disease, and he named these
particles Viruses.
Tobacco Leaf
Tobacco Mosaic Virus

4. • Wendell Stanley
 In 1935, isolated crystals of tobacco mosaic
virus. Since living organisms do not crystallize,
Stanley inferred that viruses were not truly alive.
 Reed : Discovered the first human virus, Yellow
fever virus.
 Twort : Discovered bacteriophage.
 Schope : Discovered the first influenza virus in
pigs.

5. Properties of Viruses
• They do not have cellular organization.
• They contain only one type of nucleic acid either DNA or
RNA But never both.
• They are obligate intracellular parasites.
• They lack enzymes for protein synthesis.
• They multiply by complex process but not by binary
fission.
• They are unaffected by antibacterial antibiotics.

6. Morphology of Viruses
 Viruses are acellular that means they do not have cells as it has no nucleus,
cytoplasm or any organelles.
 They need living host to survive.
 Smallest infectious virus is 20 nm (Parvovirus) to 300 nm (Poxvirus).
 They may be single or double stranded.
 The nucleic acid is linear or circular and either segmented or non-
segmented.
 Viruses spread in many ways. Just as many viruses are very specific as to
which host species or tissue they attack.
 Plant viruses are often spread from plant to plant by insects and other
organisms, known as vectors.

7.  Viruses such as influenza are spread through the air by droplets of moisture
when people cough or sneeze.
 Antibiotics have no effect on viruses, but antiviral drugs have been developed to
treat life threatening infections.
 Dengue virus, are spread by blood-sucking insects.
 Rotavirus is often spread by direct contact with infected children.
 Vaccines that produce lifelong immunity can prevent some viral infections.

8. Structure Of Virus
Viral components
• Nucleic acids
• Capsid
• Envelope
• Spikes

9. Viral Nucleic Acid
 Viruses contain a single kind of nucleic acid either DNA or RNA
which encodes the genetic information necessary for replication
of the virus.
 The genome may be single stranded or double stranded, circular
or linear, segmented or non-segmented.
 According to nucleic acid present, viruses can be classified as –
o DNA viruses
o RNA viruses

10. Viral Capsid
 Viruses consists of nucleic acid core
surrounded by a protein called capsid.
 Capsid is composed of large number of
capsomers which is made up of polypeptide
molecules.
 The capsid with the enclosed nucleic acid is
known as nucleocapsid.

11.  It serves as antigenic determinants.
 It induces antibody production.
 It provides the structural symmetry of the virus.
 It facilitates the assembly and packaging of viral genetic information.
 It serves as a vehicle of transmission from host to another.
 It protects the genetic materials.
Functions of Viral Capsid
• SPIKES - Carbohydrate-protein complexes (glycoproteins) that project
from the envelope.
 Can be used to attach to host cell.

12. Viral Envelope
 It is a lipoprotein derived from the host cell membrane and virus
specific protein.
 It is composed of glycoproteins which look like spikes.
 It confers instability to the virus because of the loss of infectivity due
to disruption of lipid.
 They are more sensitive to heat, lipid solvents and detergents.
 Examples :- Herpes virus, HIV virus, Hepatitis virus etc.

13. Viral Structure : General Morphology
 Enveloped Viruses - can be helical or
polyhedral, but the capsid is surrounded by
an envelope
 Helical : influenza virus
 Polyhedral (icosahedral) : Herpes simplex
virus
 Non Enveloped Virus -
 Viruses which does not have outer
covering.
 Naked viruses are more likely to be
resistant to lipid solvents like ether,
chloroform and detergent.
Viral Envelope : Structure

14. Viral Symmetry
1. Icosahedral Symmetry : Capsomeres are
arranged in 20 triangles
 Example : Adeno virus.
2. Helical Symmetry : They are arranged in
a
hollow coil that appears rod shaped.
 Examples : Influenza virus, Rabies virus
etc.
Tobacco mosaic virus (rod shaped)

15. 3. Complex Symmetry : Viruses which
do not show either icosahedral or
helical symmetry due to complexity of
their structure are referred to have
complex symmetry.
 Examples : Pox viruses,
Bacteriophage.

16. Classification Of Viruses
 Classification on the basis of nucleic acid
 Classification on the basis of Host
 Baltimore Classification

19. Classification on the basis of Host
• Animal viruses :
 Viruses of animal host.
 Examples : Rabies, Polio, Mumps, Chicken pox, Small pox, and
Influenza.
• Plant Viruses :
 Viruses which show their live characteristics when attached to
plants.
 Examples : Tobacco mosaic virus (TMV)
• Insect virus :
 Virus that infects insects.
 Examples : Baculovirus, Sacbrood virus, Granulosis virus.

20.  Bacterial Virus : Bacteriophages ( T1, T2, T3,
and T4.)
 Viruses that infect bacterial cells are called
bacteriophages (phages for short), which
‘bacteria eaters.’
 These are large, complex viruses, with a
characteristic head and tail structure
 The double-stranded, linear DNA genome
contains over 100 genes, and is contained
the icosahedral head.

21. Baltimore Classification
 7 groups were made.
 Its principles are fundamental to an understanding of virus classification and
genome replication.
 The Baltimore classification has + RNA as its central point.
1. dsDNA viruses (e.g. Adenoviruses, Herpesviruses, Poxviruses)
2. ssDNA viruses (e.g. Parvoviruses)
3. dsRNA viruses (e.g. Reoviruses)
4. (+)ssRNA viruses (+ strand or sense) RNA (e.g. Picornaviruses, Togaviruses)
5. (−)ssRNA viruses (− strand or antisense) RNA (e.g. Orthomyxoviruses,
Rhabdoviruses)
6. ssRNA viruses (+ strand or sense) RNA with DNA intermediate in life-cycle
(e.g.Retroviruses)
7. dsDNA viruses (e.g. Heptadnaviruses)