Nature and Properties of Viruses

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Nature and Properties of Viruses
1. Viruses are small 2. Viruses are obligate
intracellular parasites 3. Viruses contain only
one type of nucleic acid, DNA or RNA 4.
Chemical composition of viruses 5. The flow of
information in virus replication 6. Viral
replication involves disassembly of the infecting
virus and assembly of progeny virions from
protein subunits and the viral nucleic acid
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Steps in Virus Replication
1. Adsorption 2. Entry 3. Synthesis of proteins
which make the viral RNA or DNA 4. Replication of
the genome 5. Synthesis of the structural
proteins 6. Packaging of the genome i.e.
assembly of the nucleocapsid 7. Release of
virus from the cell
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Properties of Viruses Used for Classification
1. Nature of nucleic acid in genome 2. Genome
size and organization strategy of replication 3.
Symmetry and structure of the nucleocapsid 4.
Presence or absence of an envelope 5. Size and
morphology of virus 6. (Sequence similarities of
nucleic acids and proteins) 7. (Antigenic
relationships) 8. (Biological properties)
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Family Groups of Viruses
Group I ds DNA viruses Group II ss DNA
viruses Group III ds RNA viruses Group IV ss
() sense RNA viruses Group V ss (-) sense RNA
viruses Group VI Reverse transcribing RNA
viruses Group VII Reverse transcribing DNA
viruses Subviral Agents Satellites, Viroids,
Prions
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Mimivirus