Viruses are one of the most numerous microorganisms on our earth and infect all types of cells (such as human cells, animal cells, plant cells, bacterial cells and fungal cells etc). So, viruses are interesting microbes to study for what they can tell us about the genetics and biochemistry of cellular mechanisms and about the process to develop a disease.
General Characteristics of Viruses:
1. They do not occur free in nature but act as obligate intracellular parasite.
2. They are too microscopic to be seen with naked eyes.
3. They have sizes ranging from 0.02-0.3 µm (20-300nm).
4. They can’t be filtered by bacterial filters. They can pass this filters easily.
5. The genetic material of virus is either DNA or RNA but not both. This genetic material occurs in the form of single molecule and can be single or double stranded.
6. They are acellular. That is; they lack nucleus, protoplasm and cell organelles.
7. Viruses are consist of nucleic acid (DNA/RNA) and protein (capsid). They have diverse genome structures.
8. Despite having diverse genome structure, virus shows central dogma of molecular biology; “genetic information can be passed from nucleic acid to protein”.
9. The virus particle is known as virion which lack functional anatomy.
10. They lack their own enzyme system but interact with host enzyme system and synthesize new virus particles.
11. They show replication inside the host cell and thereby produce new viruses. They can replicate only using host cell machinery.
12. Virus can exist in either extracellular or intracellular form.
13. In extracellular form, they act as inanimate matter.
14. They can’t be cultured on artificial media.
15. They show no sensitivity to antibiotics. That is; they can’t be destroyed by antibiotics.
16. They can survive in pH ranging from 5 to 9.
17. They can be inert by treatment with UV lights and Hydrogen peroxides.
18. They show response towards temperature, radiation and chemical substances.
19. They can be crystallized.
20. They are sensitive to interferon, an antiviral protein.
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