Structure and Classification of Viruses

Structure and
Classification of Viruses
Properties of Microorganisms and Viruses
Non-Living
Media
Binary Fission
DNA and
RNA
Ribosomes
Antibiotics
Interferon
Bacteria
+
+
+
+
+
-
Mycoplasmas
+
+
+
+
+
-
Rickettsiae
-
+
+
+
+
-
Chlamydiae
-
+
+
+
+
+
Viruses
-
-
-
-
-
+
Structure of the Viruses
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Family
DNA Viruses
RNA Viruses
1.
Hepadnaviridae
1.
Picornaviridae
2.
Papovaviridae
2.
Calciviridae
3.
Adenoviridae
3.
Togaviridae
4.
Herpesviridae
4.
Flaviviridae
5.
Poxviridae
5.
Orthomyxoviridae
6.
Parvoviridae
6.
Paramyxoviridae
7.
Coronaviridae
8.
Arenaviridae
9.
Bunnyaviridae
10. Retoviridae
11. Rhabdoviridae
12. Reoviridae
13. Filoviridae
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Viral Symmetry
Virion Has:
1. Icosahedral Symmetry
2. Helical Symmetry
3. Complex structure
5
1. Icosahedral Symmetry:
12 Vertices + 20 Triangle Faces
Hexamers: Relation of Six Neighboring Capsomers
Pentamers: Relation of five neighboring Capsomers
Ex.Herpes, Adeno, Hepadna, Picorna, Reoviruses
2. Helical Symmetry:
Capsomers and N.A. are wound together into a coil
Lipoprotein envelope surrounded
Ex.Orthomyxo, Paramyco, Retro, Rhabdo, Coronaviruses
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3. Complex Structure:
Large (300 nm), complicated structure
Brick-shaped with core and lateral bodies, Env.
Ex.Poxviruses (Small Pox, Orf, Molluscum Contagiosum
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Icosahedral Structure:
8
Icosahedral Virus:
9
Viral Structure:
10
EM for Smallpox Virus
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Viral Structure
1. Nucleic Acid (NA):
DNA or RNA (SS,DS)
2. Capsid: Protein Coat surround the NA
NA + CAPSID
Nucleocapsid
3. Capsomers:
Form the Capsid
Polypeptide Chains
EM Shows Arrangement: Dimer
Hexamer
4. Envelope:
In some viruses
Lipoprotein
Cell Membrane Derived
Contain Viral Ags
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Viral Structure
1. Nucleic Acid (NA):
DNA or RNA (SS,DS)
2. Capsid: Protein Coat surround the NA
NA + CAPSID
Nucleocapsid
3. Capsomers:
Form the Capsid
Polypeptide Chains
EM Shows Arrangement: Dimer
Hexamer
4. Envelope:
In some viruses
Lipoprotein
Cell Membrane Derived
Contain Viral Ags
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Envelope:
1. Loose structure, derived from cell membrane
2. Virus released from infected cells by budding
3. In some viruses (Herpes, Orthomyxo, Paramyxo, Rhabdo)
4. Consist of Lipoprotein
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Protein
1. Major Constituent of all viruses
2. Protection coat for N.A.
3. Has antigenic determinants which Abs react with
4. Helps in attachment
5. Has some enzymes (Transcriptase, Thymidine
Kinase, DNA-dependent DNA polymerase) for
synthesis of DNA and mRNA.
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DNA: Deoxyribonucleic Acid
1. Mol. Wt.: 1.5 x 106 (Parvovirus) to 200 x 106
(Poxvirus)
2. Quite fragile if removed from their protein
3. Encode genetic information for replication
4. All DNA viruses are DS except parvoviruses
5. May be circular DNA (Papovavirus, Hepadnavirus) or
Linear (Adeno, Herpes, Poxyvirus)
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RNA: Ribonucleic Acid
1. Mol. Wt.: 2 x 106 (Parvovirus) to 15 x 106 (reovirus)
2. Quite fragile if removed from their protein
3. Encode genetic information for replication
4. All RNA viruses are SS except reoviruses
5. All are linear
6. Polarity (+): Ex. (Picorna, Retro, Corona, Toga),
RNA serve as mRNA
7. Polatriry (-): Ex: (Rhabdo, Orthomyxo, Paramyxo),
mRNA is transcribed from RNA by Transcriptase.
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Virus Replication
1.
2.
3.
4.
Adsorption:
To specific receptor, at 37oC Quite E
All RNA viruses are ESS except reoviruses
Entry:
Invagination of cell membrane
Syncytia and fusion
Uncoating:
Strip off protein coat by cell enzyme
Release of N/A
Translation:
Production of early and late virus mRNA
Carried by Host cell or virus enzyme
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Virus Replication (Contd.)
5.
Translation:
Virus mRNA Translated Into:
6.
7.
8.
Structural Protein (Form the Virus)
Non-structural protein (enzymes)
N/A Synthesis:
New Genomes synthesized by DNA Polymerase or
RNA Polymerase
Assembly:
N/A + Protein
In Nucleus, Cytoplasm, Plasma Membrane
New Virus
Release:
Sudden rupture or gradual budding
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