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Viruses , Viroids and Obelisks UPSC NOTE


  • Viruses are microscopic infectious agents that can only replicate inside the living cells of an organism. 

  • They are much smaller than bacteria and cannot be seen with a light microscope.

  • They consist of a core of genetic material (either DNA or RNA), surrounded by a protective protein coat called a capsid.

  • Some viruses also have an additional outer envelope made of lipids.

  • Viruses cannot reproduce on their own. 

  • They need to invade a host cell and use its machinery to make copies of themselves.

  • Once inside the cell, the virus takes over the host's machinery and reprograms it to produce viral components.

  • These components then assemble into new viruses, which can then burst out of the cell and infect other cells.

  • Viruses can cause a variety of diseases in humans, animals, and plants.

  • Some common human viral diseases include the common cold, influenza (flu), COVID-19, and HIV/AIDS.

  • Not all viruses are harmful, however. Some viruses can even be beneficial, such as those used in phage therapy to treat bacterial infections.


  • Viroids are infectious agents even smaller than viruses, but unlike viruses, they lack a protein coat. 

  • They are essentially short, single-stranded pieces of circular RNA (ribonucleic acid) that can infect plants and cause disease. 

  • As mentioned, viroids are much smaller than viruses and consist only of a single strand of circular RNA.

  • They lack a protein coat entirely, which is a key difference between them and viruses.

  • Similar to viruses, viroids cannot reproduce on their own. 

  • They need to invade a host plant cell and utilize its machinery to replicate themselves.

  • Once inside the plant cell, viroids manipulate the host's machinery to produce copies of their own RNA.

  • These new RNA molecules then fold into the characteristic circular shape and become new viroids, which can then infect other plant cells.

  • Viroids can cause a variety of diseases in plants, affecting their growth, development, and yield.

  • Some examples of viroid-induced diseases include potato spindle tuber disease, citrus exocortis disease, and avocado sunblotch viroid.

  • While not all viroids are harmful, their impact on agriculture can be significant.


  • Size: They are even smaller than viruses, consisting of circular RNA molecules around 1000 base pairs in length.

  • Shape: Their RNA folds into a rod-like structure, hence the name "obelisk."

  • Proteins: Interestingly, unlike viroids (another small RNA entity), obelisks can be translated into proteins called "oblins." These proteins have yet to be fully understood.

  • Classification: Their exact classification is still being debated. They lack the protein coat typically associated with viruses and are distinct from known viroids.

  • Origin and function: Scientists are still trying to understand where they come from, how they interact with their host organisms, and potential effects on human health.



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Learnerz IAS | Concept oriented UPSC Classes in Malayalam: Viruses , Viroids and Obelisks UPSC NOTE
Viruses , Viroids and Obelisks UPSC NOTE
Learnerz IAS | Concept oriented UPSC Classes in Malayalam
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