Overlook on VIRUSES….!!!



  • What are viruses
  • Their nature
  • Uses

When we hear word viruses, we take it so lightly. We never think about the meaning of this word. So lets first clear the concept of viruses. First question we have to see that –

  • What are viruses?
  • The answer is – Viruses are define as the tiny organism living on the border line between living and non living. Viruses consist a portion of properties like an organism but they are parasitic chemicals and segments of DNA or RNA wrapped in a coat of protein. They are unable to reproduce by their own , they require living cell to reproduce and because of this property they are not considered alive by biologist.

Viruses vary greatly in appearance and size.

Smallest size- 17nm in diameter

Largest size – upto 1000nm(1micrometer)

Largest viruses are barely visible with a light microscope , but for detailed morphological study electron microscope use is the best.

  • Next is about the discovery of viruses?
  • Every good discovery firstly face oppositions , same like this near the end of nineteenth century biologists was not accepting the existence of viruses. European scientist was attempting to isolate the infectious agent responsible for hoof and mouth disease in cattle was got a conclusion that , the infectious agent is smaller than bacterium and not get multiply in a solutions but requires a living cell to reproduce. This infecting agents were called Viruses .

But in 1993 true nature of viruses get discovered by Wendell Stanley. He discovered the exact structure of TMV(tobacco mosaic virus). TMV was like a chemical rather than an organism. So he concluded that TMV is a chemical matter rather than a living organism and after few years other scientist found that the Stanley was right. TMV virus is literally mixture  of two chemicals RNA and protein.

  • Next is Viral structure?
  • Viral structure consists- 1) a core of nucleic acid surrounded by protein.

Individual viruses contain only a single type of nucleic acid either DNA or RNA. DNA or RNA genome may be linear or circular , single stranded or double stranded.

2) protein sheath called capsid around their nucleic acid core. Capsid is composed of one – few different protein molecules. In  some  viruses some specialized enzymes are stored within capsid. Capsid protects nucleic acid from cleaving by enzymes. It also makes easier attachment with host cell by consisting special sites on its surface. It also consists penetrating proteins which penetrate host cell membrane for entering the viral genome into the host

3) Envelop – many viruses consists envelop around capsid. Envelop is rich in protein , lipids and glycoprotein molecule.  Some part of envelop is derived from a material of hosts cell and also that virus. It helps  virus to avoid the host immune system. So that it can be appear as a hosts particle and not as a foreign particle and get escaped from immune attack. Glycoprotein also helps to identify and bind to the hosts receptors sites .so that virus can bind to the hosts cell , fuse with it and allows to enter capsid and viral genome into the host and infect the host.

  • Viral shape- 1) Rod like – Tobamovirus

2) Icosahedra l- T 7 phage

3)Spherical – Rince tungro spherical virus

  • Lets see the example of virus-
  • Bacteriophage – Bacteriophage is the good example of virus which causes infection to the bacteria. They  infect bacteria , diverse structurally and functionally in bacterial host cell. These are large , complex structure with large amount of DNA and protein. Overall structure is devided into – 1)Head- icosahedral

2)capsid- consists 3 protein

3) connecting neck with a collar and long whiskers

4) long tail

5) complex base plate

Some Bacteriophages named as members of T series. T1, T2….& so forth. T3 &T7 are icosahedral and have short tails. T-even phages (T2 ,T4 & T6) have all these parts as mentioned above .

  • some diseases and their causative viruses-
  • Human Viruses-
Sr no. Disease Virus  Name













Chicken pox




Yellow fever





HIV (human immune deficiency virus)


Human herpes virus-3


Polio virus


Flavi virus




Herpes simplex virus


  • Plant viruses
Sr no. virus infection







Barley yellow dwarf


Bud blight

Infect tobacco , potato , tomato


Infect grains


Infect soyabean


  • Uses of viruses – Viruses are infectious agents . They can cause infection to healthy living organisms  like animal, plants, bacteria. They causes infection but they also helps to get rid off from many infections. They are bad but also good . They are enemies for us but also act as a friend  for us.

Many viruses   are useful biologically , economically , in medicine , in nanotechnology , in agriculture , in vaccine making. Some examples of viruses which are useful , helpful  to us as follows-

1)Cowpox virus is helpful virus . its vaccine gives immunity against smallpox

2)some virus infection like in hepatitis  -A   is helpful to suppress the infection of hepatitis –C & hepatitis –C virus suppress the replication of HIV-1.

3)some viruses also used in an anti-cancer therapy. RNA viruses have this anti –cancer capacity . we can take another example of Seneca Valley Virus 001 (RNA virus , non enveloped, Picornaviridea family) have ability to kill cancerous cells. It is more effective than Chemotherapy.

4) Viruses are also usefull in Vaccine preparation. Well known example is polio vaccine is made up of polio virus, cow pox vaccine is made up of cow pox virus.

5) Viruses are also usefull in genetic studies.

6) Genetic disorders can be treated with the help of viruses. Good example of this is retroviruses are used in treating the combined immunodeficiency disorder in small babies.

7) Viruses can kill bacteria (bacteriophages) can be used in pest control. Also disease like dysentery can be treated with the killing E-coli   by T2 bacteriophage.

In Genetic engineering   viruses acts as a model for genome sequencing.

This is all about the Viruses