Question

Viroids differ from viruses in having?
A. RNA molecules without protein coat
B. DNA molecules with protein coat
C. DNA molecules without protein coat
D. RNA molecules with protein coat

Answer 1

Viroids are the smallest self replicating RNA particles which are devoid of protein coat while viruses can have either RNA or DNA molecules encapsulated in a protein coat. Viroids were first discovered by Diener (1971).

Complete answer:
Viroids are infectious RNA particles which are smaller compared to a virus. They are obligate parasites. They consist of only the nucleic acid without a protein coat. Viruses are an infective agent consisting of a nucleic acid molecule in a proteinaceous covering known as capsid. The capsid is made up of a number of subunits called capsomeres or capsomers.
Viroids differ from viruses in the following ways:
Its RNA molecules do not code for protein. Due to this, the mechanism of disease production by viroids is still not very clear.
It lives within the cells as RNA particles only with no protein coat or capsid.
It has only one circular or linear RNA strand with very few nucleotides
As compared to viruses, viroids are known to cause diseases in plants only like potato spindle tuber, chrysanthemum stunt, etc. Animal or human infection is not known. Viruses are known to infect all types of organisms like plants, animals and humans.
Contrary to viruses in which the RNA can be copied in the nucleus or cytoplasm, the RNA of viroids are copied in the nucleus only.

So, the correct answer is option A.

Note: Viroids are basically the free RNA molecules of low molecular weight without any protein coat while viruses can have either RNA or DNA molecules encapsulated in a protein coat.