Viruses
Viruses are particles composed of an internal core
containing either DNA or RNA (but not both) covered by a protective protein
coat. Viruses are small sized living
organisms, they reproduce by replication and responsible for a wide range of
infection.
Examples : Pox virus,
-
Hepatitis virus.
-
Polio virus.
-
Herpes virus.
General Characters:
-
Very small in size
about 18 to 300 nanometer (mm)
-
Must grow inside the
living host cell.
-
Contain either DNA or
RNA.
-
Ribosome absent.
-
Energy yielding enzyme
absent.
-
Inactivated by50 -60
°C for 30 minutes.
-
They can’t grow on
inanimate culture media.
-
Optimum Ph for viruses lies between 5 to 9
-
Multiply by
replication.
-
Viruses are generally
resistant to antibiotics but sensitive to interferon’s
Morphology :
- Shape:
May be spherical, coiled,
filamentous,
- Size
: From 18-300 nm.
- Structure
: Viruses consists of-
a.
Core- contain either
DNA or RNA.
b.
Capsid –A protein coat, capsid with capsomeres.
c.
Envelope-Outer part of
capsid composed of lipoprotein , certain virus have envelope.
- Optimum
Ph : viruses lies between Ph-5 to 9.
- Inactive
: By heat at 50-60°C for 30
minutes.
- Multiply
; By replication.
Classification:
- According
to nucleic acid:
- DNA
Viruses
Examples:
-Pox virus.
- Parvo virus.
- Papova virus
- Herpes virus.
-Adeno virus etc.
2. RNA Viruses
Examples:
-
Rabies virus
-
Reo virus
-
Retro virus
-
Dengue virus.
-
Toga virus etc.
- On
the basis of strandedness:
- Double
stranded viruses
Examples:
-Pox virus
- Papova virus.
- Herpes virus.
- Adeno virus
- Rota virus.
- Small –pox virus etc.
2. Single stranded
viruses
Examples:
-Rabies virus
- Retro virus
- Dengue virus
- Toga virus etc.
C. On the basis of host range:
1. Animal viruses e.g. Rabies virus.
2. Plant viruses e.g. Tobacco Mosaic Virus (TMV)
3. Bacteria viruses(Bacteriophage)e,g T2 Phage.
4. Human viruses e.g. polio virus.
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