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  • Context (TH): Researchers recently discovered obelisks, which are biological entities within the human mouth and gut.
  • Next-generation sequencing (NGS) was employed to analyze existing datasets from human microbiomes, facilitating the discovery of obelisks.
  • NGS technology determines nucleotide sequences in genomes or specific DNA/RNA regions, enabling efficient, simultaneous sequencing of multiple fragments from diverse organisms.

What are Obelisks?

  • Obelisks are circular bits of genetic material containing one or two genes, self-organizing into a rod-like shape.
  • The Obelisks’ genetic sequences are only around 1,000 characters (nucleotides) in size.
  • They are made of RNA and proteins which facilitates self-replication within bacterial cells. Obelisks rely on microbial host cells, possibly bacteria or fungi, for replication.
  • Obelisk genes perform identical functions across diverse bacterial strains.
  • They are capable of vertically propagating from parent to offspring cells along with the host bacteria.
  • Integrate loosely into the bacterial genome without disrupting standard cellular mechanisms.
  • Obelisks fall between viruses and viroids in terms of classification.
  • Similar to viroids, obelisks are circular single-stranded RNA genomes without a protein coat.
  • Like viruses, obelisks contain genes predicted to code for proteins.

What is the difference between viruses and viroids?

Features Viruses Viroids
Structure Nucleic acid core (DNA or RNA) surrounded by a protein coat (capsid) Short, circular RNA molecule (250-400 nucleotides)
Living or Non-Living? Non-living;

lack cellular structures and independent metabolic processes


lack protein coats and protein-encoding capability

Replication Require host cells for replication, hijack host machinery Replicate within host cells using cellular enzymes
Genetic Material DNA or RNA RNA
Protein Synthesis Do not synthesize proteins independently; rely on host cells Do not encode proteins
Pathogenicity Infect animals, plants, and other organisms Infect plants and cause plant diseases
Examples Influenza virus, HIV, SARS-CoV-2 Potato spindle tuber viroid, Coconut cadang-cadang viroid

To know more about Viruses and Viroids, refer to PMF IAS CA June 5, 2021.

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