Question

Study the given figure of structure of TMV( tobacco mosaic virus ) and select the option that correctly identifies the labeling A and B.

A. A-ssDNA,B-capsomeres
B. A-dsDNA,B- capsomeres
C. A-ssRNA,B – capsomeres
D. AdsRNA, B- tail fibers

Answer 1

Hint: Tobacco mosaic virus has a rod like appearance and it has a capsid made up of coat protein. They are generally found in parts of plants except at the tip of growing points.

Complete Answer:
Tobacco mosaic virus or TMV is a positive single stranded RNA virus species in the genus Tobamovirus that infect a broad range of plants, particularly tobacco and other members of the family Solanaceae. The infection causes typical patterns such as mosaic -like mottling and discoloration on the leaves. TMV was the first virus to be discovered. Even though it was known from the late 19th century as a non-bacterial infectious disease damaging tobacco crops.

Tobacco mosaic virus has a rod-like shape. Its capsid is made up of 2130 molecules of coat protein and one molecule of genomic single strand RNA, 6400 bases long. The coat protein self unites into the rod-like helical structure around the RNA, and forms a hairpin loop structure. The protein monomer is composed of 158 amino acids and are assembled into four main alpha-helices, which are connected by a prominent loop proximal to the axis of the virion.

Virions are about 300 nm in length and 18 nm in diameter. Negatively stained electron microphotographs explain a distinct inner channel of radius 2 nm. The RNA is situated at a radius of 4 nm and is secluded from the action of cellular enzymes by the coat protein. X-ray fiber diffraction structure of the whole virus was studied based on an electron density map at about 3.6 Å resolution. Within the capsid helix adjacent to the core, is the coiled RNA molecule, which is made up of 6,395 ±10 nucleotides.

So the correct answer for this question is option C) A-ssRNA, B – capsomeres.

Note: TMV virus was the first RNA containing virus of plants which have its genome completely sequenced. They also play a major role in phytopathology.