Properties - Physical, Chemical, biological properties of virus - Dr. S. Sivasankara Narayani

1. Microbial Taxonomy and Diversity –
Physical , Chemical and Biological
Properties of Virus
Dr. S. Sivasankara Narayani
Assistant Professor
Department of Microbiology
Ayya Nadar Janaki Ammal College
Sivakasi
29-08-2020
Dr.SS

2. UNIT–III
CLASSIFICATION
OFVIRUS
 Viruses: Physical, chemical and biological properties.
Baltimore classification. Types of viruses based on
structure and Host. Cultivation of viruses: Cell line -
embryonated eggs - cytopathic effect. Structure of
viruses: TMV- T4bacteriophage. Replication of virus:
Lytic and lysogenic cycle. Phage typing.
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3. Introduction
 A virus is an infectious agent of small size and
simple composition that can multiply only in living
cells of animals, plants, or bacteria.
 The name is from a Latin word meaning “slimy liquid”
or “poison.”
 A virus particle is made up of genetic material housed
inside a protein shell, or capsid.
 The genetic material, or genome, of a virus may consist
of single-stranded or double-stranded DNA or RNA and
may be linear or circular in form.
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4. Intro
 The infective, extracellular (outside the cell) form of a
virus is called the virion.
 Viroids (meaning “virus like”) are disease-causing
organisms that contain only nucleic acid and have no
structural proteins.
 Other virus like particles called prions are composed
primarily of a protein tightly complexed with a small
nucleic acid molecule.
 Prions are very resistant to inactivation and appear to
cause degenerative brain disease in mammals,
including humans.
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5. History
 In 1892 by the Russian scientist Dmitry I. Ivanovsky and
in 1898 by the Dutch scientist Martinus W. Beijerinck.
 Beijerinck - infectious agent, which he
designated contagium vivum fluidum, meaning - live,
reproducing organism that differed from other organisms.
 Both of these investigators found that
a disease of tobacco plants could be transmitted by an
agent, later called tobacco mosaic virus
 In 1915 by the British investigator Frederick W. Twort
and In 1917 by the French Canadian scientist Félix H.
d’Hérelle, lesions in cultures of bacteria -
bacteriophage (“eater of bacteria”),
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6. History
 Wilson Smith, Christopher H. Andrewes, and Patrick P.
Laidlaw - influenza
 In 1941 the American scientist George K. Hirst found
that influenza virus - chicken embryo could be
detected by its capacity to agglutinate (draw together)
red blood cells.
 American scientists John Enders, Thomas Weller,
and Frederick Robbins, who in 1949 developed the
technique of culturing cells on glass surfaces; cells
could then be infected with the viruses that
cause polio (poliovirus) and other diseases
 The American scientist Renato Dulbecco in 1952 -
plaques in layers of adjoining animal cells overlaid
with agar
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7. Propertiesof
Virus
Physical
Chemical
Biological
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8. Physical
 Size
 Shape
 Capsid
 Symmetry
 Envelope
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9. Size
20-300nm in diameter
Parvovirus -smallest Size-20nm
Poxvirus-Largest Size-400nm
Plant viruses-17-200nm
Animal viruses-20-350nm
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10. Shape
Rod shaped- TMV
Brick shaped- pox virus
Bullet shaped- Rabies virus
Spherical shaped- HIV, Influenza
Tadpole shaped- Bacteriophages
Some viruses are irregular &
Pleomorphic Shape
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12. Capsid
The nucleic acid of a virus is
surrounded by a protein coat called
the capsid.
Each capsid is composed of a large
number of protein subunits
(polypeptides) calledcapsomeres,
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13. Capsid
 The helical viruses appear rod-like and may be rigid or
flexible. The viral genome is found within hollow cylin-
drical capsid that has a helical structure. Ex: rabies virus,
Ebola hemorrhagic virus, etc.
 The polyhedral viruses appear as many-sided viruses. The
viruses consist of capsids in the shape of an icosahedron.
It is a regular polyhedron with 20 triangular faces. The
capsomere of each face forms an equilateral triangle. - Ex:
Adenovirus.
 The helical and polyhedral viruses whencovered by
envelope are called as enveloped helical or enveloped
polyhedral viruses, respectively. Ex: Influenza virus -
enveloped helical virus , Herpes simplex virus - enveloped
polyhedral virus.
 Some viruses, such as viruses of bacteria(e.g.,
bacteriophages), have complicated structures and are
called complex viruses
Helical viruses
Polyhedral viruses
Enveloped viruses
Complex viruses
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14. Envelope
Nucleocapsid is covered by a lipoprotein membrane.
In some viruses, the capsid is covered by an envelope,
such viruses are called enveloped viruses
It may contain glycoprotein – spikes [or] peplomers .
More than one type of spikes – Influenza
Triangular – hemagglutinin
Mushroom shaped – neuraminidase
All of the negative-stranded RNA viruses are enveloped.
The viruses that lack envelope - nonenveloped or naked
viruses
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15. Symmetry
Three types of symmetry are observed
depending on the arrangement of the
capsid around the nucleic acid core
(genome).
(a) icosahedral (cubical)
(b) Helical
(c) complex symmetry.
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16. Symmetry–
Icosahedral
 Two types of capsomeres constitute the icosahedral
capsule.
 pentagonal capsomeres or the vertices (pentons) and
 hexagonal capsomeres making up the facets (hexons)
 There are always 12 pentons
 number of hexons varies with the virus group.
 Each penton has fivefold symmetry (pentamer or
pentagon) in the shape of an equilateral triangle . Ex
picornaviruses and parvoviruse
 picornaviruses, each pentamer is made up of five
protomers, each of which is composed of three subunits
of four different proteins.
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17.  The hexamer symmetry - large capsid virions, -
herpesviruses and adenoviruses.
 Hexons are made up of certain structurally distinct
capsomeres between the pentons at the vertices.
 The presence of hexon extends the icosahedral and is
called an icosadeltahedral.
 The adenovirus nucleocapsid has 12 pentons and 240
hexons
 The herpesvirus nucleocapsid has 12 pentons and 150
hexons surrounded by an envelope.
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18. Helical
 The nucleic acid and the capsomeres are wound
together to form a spherical or spiral tube.
 The viruses with helical structure usually appear as
rods and their capsomeres self-assemble on the RNA
genome into rods extending to the length of the
genome.
 These capsomeres cover and protect the RNA.
 The tubular nucleocapsid structure may be rigid as in
tobacco mosaic virus, but may be pliable and may be
coiled on itself in case of some other animal viruses.
 Helical nucleocapsids are usually demonstrated within
the envelope of most negative-stranded RNA viruses.
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19. Complex
symmetry
 Some viruses may not exhibit either icosahedral or
helical symmetry but instead may exhibit a complex
symmetry – Ex- poxvirus shows a complex symmetry.
◗ Shape
 Most of the enveloped viruses are round or pleomorphic
with exception of poxvirus and rhabdovirus.
 Rhabdovirus- bullet-shaped virus
 poxvirus - brick shaped.
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20. Chemical–
DNA,RNA,
enzymes
 I: dsDNA viruses (e.g. Adenoviruses, Herpesviruses,
Poxviruses)
 II: ssDNA viruses (+)sense DNA (e.g. Parvoviruses)
 III: dsRNA viruses (e.g. Reoviruses)
 IV: (+)ssRNA viruses (+)sense RNA (e.g.
Picornaviruses, Togaviruses)
 V: (−)ssRNA viruses (−)sense RNA (e.g.
Orthomyxoviruses, Rhabdoviruses)
 VI: ssRNA-RT viruses (+)sense RNA with DNA
intermediate in life-cycle (e.g. Retroviruses)
 VII: dsDNA-RT viruses (e.g. Hepadnaviruses)
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21. Enzymesand
Protein
 Glycoprotein
 Viral proteins
 RNA dependent RNA Polymerase
 Neuraminidase
 Reverse Transcriptase
 Some other proteins
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22. Biological
Properties
 Viral replication can produce biochemical & structural
changes in the host cell.
 Cell damage - cytopathic effect
 Attachment - Penetration - Uncoating - Replication –
Maturation - Release
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23. Clarifications
sivasan91@gmail.com
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Dr.SS

24. Questionsto
think
 What is virus ?
 What is capsomeres?
 Chemical properties of virus!
 Classify based on symmetry
 Example for non enveloped virus
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Dr.SS