Context:
Recently, an article on Hindu |Newfound ‘obelisks’ join viruses, viroids as third unusual life form
Obelisks:
- A new form of life lying between viruses and viroids on the scale of simplicity
- It is a rod-shaped fragments of RNA that are found in gut and mouth bacteria
- Like viroids, obelisks have a circular single-stranded RNA genome
- It does not have protein coat but, like viruses, their genomes contain genes that are predicted to code for proteins
- They can still transmit instructions to cells even though they are smaller than viruses
- All obelisks encode a single major protein known as obulin
- It neither cause any harm nor benefit to their microbial host, or to humans
- The discovery was made possible using data obtained using a powerful technique called next-generation sequencing (NGS)
- The researchers linked one particular obelisk to the bacterial species Streptococcus sanguinis, commonly found in the human mouth.
Important Terms:
- Virus –
- A microscopic, non-cellular structure that consists of a nucleic acid molecule covered by a protein coat
- It is an intracellular parasite
- Virion –
- An active, infectious form of a virus outside the host cell
- It has both nucleic acid as well as protein layers
- It is an extracellular parasite
- Prion –
- A type of protein that can cause disease in animals and humans by triggering normally healthy proteins in the brain to fold abnormally
- It has no genetic material
- Viroids – A Small, single-stranded, circular RNA that do not encode any protein
- Virusoids – A Single stranded (ss) RNAs that require other helper viruses to establish an infection
Difference between viruses and viroids:
| Viruses | Viroids | |
| Composition | Nucleic acid (DNA or RNA) core that acts as the genetic material | Viroids circular single stranded RNA |
| Surrounded by | A protein coat, and, in some cases, a lipid (fat) layer outside that coat | Does not contain the lipid layer or the protein coat found in viruses |
| Size | Larger in than viroids | Smaller than viruses |
| Host | Infects both plants and animals | Infects only plants |
| Example | Tobacco mosaic virus, Hepatitis- C | Potato spindle tuber viroid |
Source: The Hindu
Previous Year Question
Which of the following statements is/are correct?
1. Viruses lack enzymes necessary for the generation of energy.
2. Viruses can be cultured in any synthetic medium.
3. Viruses are transmitted from one organism to another by biological vectors only.
Select the correct answer using the codes given below.
[UPSC Civil Services Exam – 2013 Prelims]
(a) 1 only
(b) 2 and 3 only
(c) 1 and 3 only
(d) 1, 2 and 3
Answer: (a)
Explanation:
Statement 2 is not correct:
Viruses cannot be grown in a synthetic medium like the bacteria is grown. They are grown in living cells.
Statement 3 is not correct:
Viruses are transmitted from one organism to another by both biological vectors such as mosquitoes and mechanical vectors such as flies.
