Question

Number of capsomeres in TMV is
A. 3120
B. 2130
C. 1230
D. 231

Answer 1

Hint: TMV is called the tobacco mosaic virus. It is a single-stranded RNA virus species. It affects a wide range of plants. The capsomeres are known to be the subunits of capsid which are the outer protective covering of proteins and protect the genetic material of the virus. On every three turns of the helix, there are 49 capsomeres that are present.

Complete answer:
- The capsid can be basically thought of as a shell of protein which surrounds the genome and that has subunits of proteins which are the capsomeres.
- Some viruses have not more than a genome which is surrounded by capsid. These are called nucleocapsids. Many of the animal viruses have an envelope type of structure which surrounds helical or polyhedral nucleocapsid. Therefore these are termed as enveloped viruses. Envelope is of the origin of the host. But the virus still can incorporate its own proteins which are visualized as glycoprotein spikes. They attach viruses to receptors on suitable host cells.
- Numbers of capsomeres in TMV are 2130 because on every three turns of the helix, 49 capsomeres are present on every three turns of the helix.

Hence, the correct answer is option (B).

Note: The tobacco mosaic virus is known to cause diseases in plants, symptoms of which include mottling of leaves with a patchy appearance of yellow or green color. This virus is responsible for stunted growth of plants. Plants can also have brittle leaves and unripened fruits. No vaccine is currently found for the protection of plants from TMV. But, seeds that have TMV externally can be exposed to acid extraction or trisodium phosphate whereas seeds having internal TMV can be given dry heat treatments.