Virus Biology and Their Intriguing Applications

A virus is the smallest and ultramicroscopic living particle discovered by Iwanowsky in 1892.

They can be observed only by an electron microscope.

They are viable only inside the host and are inactive outside the host cells.

Thus, one can categorize them as obligate parasites on either animal, plant, or bacterial cells.

Virus Structure & Biology

The structure of a virus is quite simple. It consists of

  1. Nucleic acid core &
  2. The protein coat (capsid).

No other cellular constituents are present except the above.

The nucleic acid core is the center of the virus particle and is usually either DNA or RNA.

This nucleic acid forming the center portion is surrounded by a protein coat termed the capsid. This capsid is made of many capsomeres.

This coat forms the bulk of viral mass and may sometimes have carbohydrates and lipids to a small extent.

virus structure
Structure of bacteriophage virus

A bacteriophage has a head, tail, collar (neck), base plate (endplate), and tail fibers.

The Head is hexagonal in shape with double-stranded DNA at the center. It is surrounded by a protein coat.

This protein coat extends into the collar, tail, and also tail fibers. There are 6 tail fibers. These help in the attachment of the virus to the bacteria.

They are so small that they can pass through bacterial filters.

Virus life cycle

There is not much to study in a virus’s life cycle except for its replication.

This multiplication happens in four stages as

a) Adsorption phase

Here, the virus particle gets attached to the bacterial cell or host cell.

Initially, the particle attaches to the bacterial wall through the ionic bonds.

This is reversible with a change in pH or salt concentration.

Later, the attachment becomes irreversible as the virus proteins on the surface link to bacterial cell surface receptors.

b) Penetration and uncoating.

The virions penetrate the cell either due to the phagocytosis mechanism of the host cell.

Once inside, the virus particles are released due to lysosomal protease.

The other way is the virus particle fuses to the host cell, and its genetic material is released into the cytoplasm of the host cell.

b) Eclipse Phase (replication and biosynthesis phase)

Here, the virus DNA takes the chromosome-forming machinery of the cell under control and directs it to produce different parts of the virus particle.

If it is an RNA virus, the viral RNA replicates in the presence of the enzyme RNA polymerase, and then it undergoes translation to form viral proteins.

c) Vegetative phase

In this stage, the virus components formed get assembled to form a new virus.

The DNA or RNA formed in the previous step are enclosed by the viral proteins forming a capsid.

d) Lytic phase:

Here, the virus particles thus formed initiate breakage of the bacterial cell and get liberated from the cell.

Applications of viruses

Viruses find their applications in research and medicine.

  1. The bacteriophages are routinely used to study different aspects of cell structures. For example, they were used to determine the composition of genetic material with DNA and not proteins in Hershey-Chase Experiments.
  2. The neurotrophic viruses like pseudorabies and poxviruses are used to study complex neural networks.
  3. Certain Oncolytic viruses are used in the treatment of cancer.
  4. Viruses like adenovirus are used as viral vectors to deliver desired genes in gene therapy.


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