The word phage means
‘eater’. A phage virus consists of nucleic acid, head, tail and end plate. The
complete, mature and infectious particle is known as virion.
Nucleic acid
The interior core is of
nucleic acid. The phage virus has DNA, which is also known as its genome.
Head
The outer coat of protein
surrounding the nucleic acid is called head. The head is hexagonal. It is made
up of protein, subunit called capsomeres. The number of capsomeres is
characteristic of a particular virus. Herpes virus 162, advnonovirus 252, in
some animal virus the nucleocapsid is covered by an envelope.
Tail
The tail is hollow, tubular
and made up of proteins. It consists of six fibers. The protein sheath around
the tail is contractile. End plate: The tail fibers are attached to end plate.
It is the last part of the tail. End or base plate has tail pins.
Classification of
Viruses
The classification of
viruses is based on their
(a) Size and shape.
(b) Presence or absence of
outer envelope.
(c) Type of nucleic acid
and whether it is a single or double strand.
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| A Phage Virus |
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| Shapes of Viruses |
Virus size
Viruses can be seen only
under electron microscope. Viruses vary in size. Have size from l7nm to l000nm.
Virus Shape
Viruses vary in shapes. The
polio virus particles are little spheres that look like tiny golf balls.
Tobacco mosaic virus is a rod shaped and helical virus, while some phage
viruses look like tadpoles.
So viruses have several
shapes, such as spherical, needle like and cubical. Most forms are icosahedral
with up to twenty sides.
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| HIV Virus |
Virus morphology and
nucleic acid properties are most important for classifying plant animal and
bacterial viruses. To provide a systematic idea about the diversity of viruses,
they have been classified into different groups.
1. Undeveloped Plus strand
RNA virus
2. Enveloped Plus strand
virus
3. Minus strand RNA virus
4. Viroids
5. Double stranded RNA
viruses
6. Small Genome DNA RNA
viruses.
7. Medium Genome and Large
Genome virus
8. Bacteriophage
what is the function of the tail fiber?
ReplyDeleteTail fiber is mainly used for the attachment to the host cell.
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