Question

Which of the following viruses is devoid of protein coat and their body is constituted by only RNA?
A. Tobacco Mosaic Virus (TMV)
B. Potato Spindle Tuber Virus (PSTV)
C. Polyomavirus
D. Mumps virus

Answer 1

Hint: Viruses are microscopic organisms. They are to infect other organisms or hosts, in which they replicate and continue their life cycle. The genetic material of viruses can be RNA or DNA. The genetic material may or may not be covered with a protein coat.

Complete answer:
> Potato Spindle Tuber Virus or PSTV is a viroid. Viroids are microorganisms containing a single stranded RNA as their genetic material. However, they lack the protein coat of viruses. PSTV(s) are known to affect potatoes and tomatoes. There are various strains of PSTV present. The typical symptoms include colour changes in the foliage, the leaves become small sized and a decreased rate of sprouting.
> Tobacco Mosaic Virus or TMV is a single stranded RNA virus. They belong to the genus Tobamovirus. The capsid or the covering of TMV is protein in nature. The protein in the capsid surrounds the single stranded RNA in rod-like helical structures. TMV primarily infects the members of family Solanaceae, especially Tobacco plants.
> Polyoma virus belongs to the family Polyomaviridae. The genetic material of these viruses is a double stranded DNA. A protein capsid covers the genetic material. Polyoma virus is known to affect human beings.
> Mumps virus is the causative agent of mumps. The genetic material of this virus is a single stranded RNA surrounded by a protein coat. The natural and only hosts of this virus are human beings. Mumps occur primarily in children. Clinical symptoms include loss of appetite, fever, headache followed by swelling of the parotid glands.
Therefore, it can be concluded that PSTV is a viroid comprising RNA as their genetic material and they lack a protein coat.

Hence, option (B) is correct.

Note: Viruses are infecting agents. The typical hosts of viruses are numerous – viruses are known to affect almost all living organisms. They have a genetic material such as DNA or RNA that are capable of self-replicating. Viruses are often transferred by vectors such as flies, mosquitoes. Viruses can also be transmitted by sneezing or coughing. Commonly known viruses are Tobacco Mosaic Virus, Mumps virus, HIV, Hepatitis virus, etc.