VIROOGY
Viruses are the smallest known as infective agents . The
genome of a virus is wither DNA or RNA . That is the only content one kind of
nucleic-acid . Viruses are metabolically inert or infective or enter into the
cell . The viruses undergoes replication and that increases in number . It does
not divided by Binary fission as in bacteria .
Structure of Virus
A virus basically consist of a core of nucleic acid ,
surrounded by a protein coat which protects the virus genome from environmental
factors . The structures which make-up a virus particle are known as (i) Virion
(ii) Capsid – which is the protein coat .
The capsid is
composed of capsomeres which is the unit
structure may surrounded by an envelope
.
Cultivation of Viruses
As viruses replicate within living cells . Special methods
are used to culture viruses like
i)
Tissue culture – cells are obtained from man or animals
are grown in artificial cultures in the laboratory and these cultures support
viral replication .
ii)
Chick embryo – Some viruses grown in cells in the chick
embryo
iii)
Laboratory animals – Different laboratory animals are
used for the replication of viruses .
Viruses can’t be grown in artificial cultures as bacteria .
Effects of virus on cells
It affects on cells in three way
i)
Cell death – It causes cytopathogenic effect which kill
the cell .
ii)
Cell transformation -
Here cell is not killed but changed from a normal cell to malignant or
cancerous cell .
iii)
Latent infection – The viruses remains in the cell in
an active state but produces minimum effects on its function .
Classification of Viruses
DNA viruses
i)
POX viruses – It causes small-pox
ii)
Herpes viruses – It causes Herpes , Chicken-pox .
iii)
Adeno viruses – It causes respiratory infections and
conjunctivitis .
iv)
Hepadna viruses – Hepatitis B virus causes Hepatitis .
RNA
viruses
i)
Rhabdo viruses – Rabbies virus
ii)
Picorna viruses – Polio virus which causes polio .
Hepatitis viruses .
iii)
Flevi virus – It causes Encephalitis .
iv)
Reo Viruses – Rota
virus which causes gastroentrities , specially in children .
v)
Retro viruses – HIV virus which causes AIDS .
Properties of Virus
i)
Heat – Viruses are usually inactivated at 56*c for
30minutes and 100*c for few seconds .
ii)
Cold – Viruses are stable at veryt low temperature even
at -70*c .
iii)
Ultra violet rays – It inactive viruses .
Viruses are usually killed by hydrochloride solution and
glutaraldehyde .
Entry of Viruses
Viruses enter the body via respiratory tract by inhalation .
some viruses however entire by ingestion or by inoculation or by the bite of a
insect . some viruses may gain entrance by sexual contact .
Viruses replication
Virus replication takes place in 7-stages
i)
Adsorption – To specific receptors on the cell/plasma
membrane .
ii)
Entry – Probably by invagination of cell membrane .
iii)
Un-coating – That is release of the virus nucleic acid
.
iv)
Transcription –
That is production of virus messenger RNA to form the viral genome – this is
carried out by the host cell or virus specified enzyme .
v)
Synthesis of virus component
vi)
Assemble – New virus genomes and proteins are assembled
to form new virus particles .
vii)
Release – Either by sudden rupture or by gradual
budding of the viruses through cell membrane .
