What are viruses and their characteristics


Viruses are non-cellular infectious particles containing only of viral genes i.e. RNA (Ribonucleic Acid) or DNA (Deoxyribonucleic Acid) enclosed in a proteinaceous coat and reproduces only in living cells.


The term virus is originate from Latin word Venom. The term Venom represent poisonous fluid. Viruses utilize bio-synthetic system i.e. Ribosomes etc. of their hosts for their own synthesis division or fusion. They can share themselves gently to other cells of host.

Characteristics of viruses

Viruses shows following characters:

  1. Size : Viruses are very small in size. They can be seen only by electron microscope.

  2. Size of Pox and Parvoviruses : The size of Pox viruses is 250 nano-meter (1 NM =10 raise to power -9). It is small pox causing virus. The size of Parvoviruses is 20 NM. It is chronic anemia causing virus.

  3. Smaller than bacteria : Viruses are 10 to 1000 times smaller than the bacteria. So they can easily pass through the filter from which bacteria cannot pass.

  4. Cannot grow artificially : Viruses cannot grow on artificial media or test tube. They can reproduce only in animals body or plants cells or microorganisms.

  5. Replication : Viruses reproduce by a process called replication. Many replicas of a virus are replicated by replication.

  6. Obligate inter-cellular parasite : The viruses are obligate inter-cellular parasite. An obligate inter-cellular parasite cannot live without its host.

  7. Lack metabolic machinery : Viruses lack metabolic machinery (enzymes). Therefore, they cannot synthesize their own nucleic acid and proteins. They depends on their hosts cells for carrying out these functions.

  8. Cannot generate energy : Viruses cannot generate or store energy in the form of ATP (adenosine triphosphate). They get their energy from from the host cells.

  9. Disease : The virus may cause disease in host cells during reproduction.

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