This set of Virology Multiple Choice Questions & Answers (MCQs) focuses on “Characteristics of Plant Viruses”.
1. Which of the following plant viruses has split genome?
a) Tobacco mosaic virus
b) Tobacco rattle virus
c) Cauliflower mosaic virus
d) Potato virus Y
View Answer
Explanation: Many plant viruses consist of two or more distinct nucleic acid strands which are enclosed within particles of different sizes made up of same protein subunits. These nucleic acids are called split genomes. Tobacco rattle virus consists of two single stranded RNA in separate capsids which resemble two rods, a long one and a shorter one. So, it has a split genome.
2. Which of the following substances is present on the surface of plant viruses?
a) Protein
b) Nucleic acid
c) Calcium
d) Nickel
View Answer
Explanation: The surface of plant viruses contains a definite number of protein subunits. The proteins are arranged spirally in the elongated viruses and packed on the sides of the polyhedral particles of the spherical viruses. The nucleic acid is present inside the shell made up of protein subunits or arranged spirally embedded between the protein subunits.
3. Which of the following plant viruses has an outer lipoprotein membrane?
a) Tobacco mosaic virus
b) Gemini virus
c) Rhabdovirus
d) Cowpea chlorotic mottle virus
View Answer
Explanation: Rhabdoviruses are provided with an outer lipoprotein envelope or membrane. The lipid envelope is formed from a portion of the host cell membrane. As the envelope is made from the host cell, it is not recognized by the host’s immune system. Thus, it protects the viral genetic material and helps in entry of the virus into the cell evading immune responses.
4. Satellite viruses can cause infection alone.
a) True
b) False
View Answer
Explanation: Satellite viruses cannot cause infection by themselves. They must always be associated with certain typical viruses called helper viruses to cause infections. Satellite viruses are dependent on the helper viruses for multiplication and plant infection. Satellite viruses act like parasites of the associated helper virus and reduce their ability to multiply and cause diseases.
5. Which of the following nitrogen bases is absent in viral RNA?
a) Adenine
b) Guanine
c) Cytosine
d) Thymine
View Answer
Explanation: In viral RNA, the four bases, adenine, guanine, cytosine and uracil are present. Adenine and guanine are purine bases and they can interact with the pyrimidine bases uracil and cytosine. In DNA the uracil base is replaced by the base methyl uracil popularly known as thymine. So, thymine is absent in RNA but present in DNA.
6. What is the morphology of rhabdoviruses?
a) Polyhedral
b) Cylindrical rods
c) Spherical
d) Isometric
View Answer
Explanation: Rhabdoviruses are short, cylindrical in structure. They are approximately three to five times as long as they are wide. They have bacillus-like morphology. Rhabdoviruses have an outer lipoprotein membrane. Inside the membrane is the nucleocapsid, consisting of nucleic acid and protein subunits.
7. What is the genetic material of Potato virus Y?
a) Single-stranded positive RNA
b) Double-stranded DNA
c) Single-stranded DNA
d) Double-stranded RNA
View Answer
Explanation: Most plant viruses contain single stranded RNA as genetic material. Potato virus Y also has single stranded positive RNA. However, plant viruses with double-stranded RNA, double-stranded DNA and single-stranded DNA as nucleic acid are also found in rare cases.
8. Which of the following plant families is the host of tobacco mosaic virus?
a) Solanaceae
b) Asteraceae
c) Liliaceae
d) Scrophulariaceae
View Answer
Explanation: Tobacco mosaic virus infects tobacco and many other Solanaceous plants. It damages the leaves, flowers, fruits of the hosts and causes severe economic loss. The Solanaceae family includes plants like tomato, petunia and pepper which are affected by the tobacco mosaic virus.
9. How many open reading frames (ORFs) are present in the RNA of Tobacco mosaic virus?
a) 5
b) 3
c) 4
d) 1
View Answer
Explanation: The genetic material of Tobacco mosaic virus is one positive single-stranded RNA of approximately 6,400 nucleotides. The RNA has four open reading frames (ORF) and it is translated into four proteins, one of which is the coat protein, two are components of the RNA polymerase enzyme, and the fourth protein is associated with the cell-to-cell movement of the virus.
10. The Tobacco mosaic virus capsid is composed of a single type of protein, 158 amino acids in length. How many nucleotides are required to code for the protein?
a) 632
b) 474
c) 158
d) 316
View Answer
Explanation: We know, 1 amino acid is encoded by 3 nucleotides.
Given, Length of capsid protein of Tobacco mosaic virus = 158 amino acids
Therefore, number of nucleotides required to encode the protein = 158*3
= 474
11. What is the shape of icosahedral capsid of virus?
a) Sphere
b) Polyhedron
c) Helical
d) Shapeless
View Answer
Explanation: The shape of icosahedral capsid is a regular polyhedron with 20 equilateral triangular faces and 12 vertices. It is constructed from ring or knob shaped units called capsomers, each usually made up of five to six protomers (capsid proteins). Icosahedral capsids can enclose a space most efficiently.
12. If plant virus X is a double stranded DNA virus with 30 percent adenine residues, what percentage of guanine residues are present in the virus genome?
a) 20
b) 40
c) 30
d) 60
View Answer
Explanation: The double stranded viral DNA has complementary base pairing and should follow Chargaff’s rule of base pairing. According to Chargaff’s rule, in any double stranded DNA the number of guanine units (G) are equal to the number of cytosine units (C) and the number of adenine units (A) are equal to the number of thymine units (T).
Given,
Percentage of A = 30
Therefore, percentage of T = percentage of A = 30
The sum of adenine, guanine, cytosine and thymine residues is equal to 100% and percentage of G = percentage of C.
Therefore,
A+G+T+C = 100%
30%+G+30%+C = 100%
60%+2G = 100% (Since, G=C)
2G = 100%-60%
= 40%
G = 40%/2
= 20%
13. What happens when a double-stranded DNA virus enters into the plant cell’s nucleus?
a) It forms a single-stranded DNA
b) It remains as double-stranded DNA
c) It forms two single-stranded RNAs
d) It forms one single stranded RNA
View Answer
Explanation: Inside the plant cell’s nucleus, viral double-stranded DNA is transcribed into two single-stranded RNAs. Among them, the smaller RNA is transported to the cytoplasm, where it is translated into virus coded proteins and the larger RNA is also transported to the same location in the cytoplasm, but it becomes encapsulated by coat protein subunits and is used as a template for reverse transcription into a complete virion double-stranded DNA.
14. What is the genetic material of Gemini viruses?
a) Single-stranded RNA
b) Single-stranded DNA
c) Double-stranded DNA
d) Double- stranded RNA
View Answer
Explanation: Gemini viruses contain circular, single-stranded DNA molecule as genetic material. It is made up of 2500 nucleotides. Gemini viruses utilize the rolling circle mechanism to replicate their genome. It is characterized by the presence of connected pair of capsids which gave it the name Gemini virus (Gemini = twins).
15. What is the difference between viroid and virus?
a) Viroid cannot cause disease
b) Viroid do not have protein coat
c) Viroid do not have nucleic acid
d) Viroid cannot infect plant cell
View Answer
Explanation: Viroid lacks a protein coat and exists as free naked RNA. Viroid can infect plant cells and cause diseases. Virus always consists of nucleic acid, either DNA or RNA, and a protein coat called the capsid. So, viroid is different from virus because viroid does not have a protein coat.
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