This set of Virology Multiple Choice Questions & Answers (MCQs) focuses on “Capsid Assembly of Viruses”.
1. Which of the following protects the viral nucleic acid?
a) Cell wall
b) Cell membrane
c) Mitochondrial membrane
d) Capsid
View Answer
Explanation: The viral nucleic acid is surrounded by a protein coat called the capsid. The main function of the capsid is to protect the viral genome. The capsid also helps in the transfer of the viral genome from one host cell to another. The capsid is produced from proteins which are encoded by the virus genome.
2. The capsid protein of tobacco mosaic virus is 158 amino acids in length. The tobacco mosaic virus genome has 6400 nucleotides. What percentage of the tobacco mosaic virus genome is used to code for the capsid?
a) 7.4
b) 2.4
c) 4.9
d) 9.8
View Answer
Explanation: It is known that 1 amino acid is encoded by 3 nucleotides.
Given,
Tobacco mosaic virus capsid protein has 158 amino acids.
Therefore, number of nucleotides required to code for the capsid protein = 158*3 = 474
The tobacco mosaic virus genome has 6400 nucleotides.
Therefore, percentage of tobacco mosaic virus genome used to encode the capsid = (474/6400) *100 = 7.4
3. Which of the following proteins is used to construct capsid of virus?
a) Protomer
b) Regulatory protein
c) Envelope protein
d) Accessory protein
View Answer
Explanation: The capsid is a protein coat that surrounds the viral nucleic acid. The proteins used for capsid formation are encoded by the virus genome. The protein subunits that form capsid are known as protomers. The protomers self-assemble to form capsid by a complex process. Non capsid proteins can be used by viruses as scaffolding upon which capsids are assembled.
4. Which of the following types of capsid symmetry is present in tobacco mosaic virus?
a) Helical
b) Icosahedral
c) Complex
d) Binal
View Answer
Explanation: Tobacco mosaic virus has helical capsid symmetry. Helical capsids have the shape of a hollow tube with protein walls. The protomers of tobacco mosaic virus self-assemble in a helical arrangement to produce a rigid tube. The RNA genome of the virus is enclosed within the capsid. It lies within a groove formed by the protein subunits.
5. Which of the following can influence the size of a helical capsid of a virus?
a) Host cell membrane
b) Nucleic acid content of virus
c) Nucleic acid content of host cell
d) Envelope of virus
View Answer
Explanation: The size of the helical capsid is influenced by the nucleic acid of the virus enclosed within the capsid and the protomers. The diameter of the capsid is dependent on the size, shape and interactions of the protomers. The length of the capsid is determined by the nucleic acid because a helical capsid cannot extend much beyond the end of the virus genome.
6. How many protomers are present in icosahedral capsids?
a) Two or three
b) One or two
c) Five or six
d) Seven or eight
View Answer
Explanation: Icosahedral capsids are produced from ring or knob shaped units called capsomers. Each capsomer is made up of five or six protomers. The pentamers have five protomers and hexamers have six protomers. The pentamers are present at the vertices of the icosahedron. The hexamers form the edges and triangular faces of the icosahedron.
7. Which type of capsid symmetry is present in poxvirus?
a) Complex
b) Icosahedral
c) Helical
d) Spherical
View Answer
Explanation: Poxvirus is a large animal virus with complex symmetry. It has an ovoid to brick-shaped exterior. The core of the virus is a central structure which is shaped like a biconcave disc and surrounded by a membrane. The double stranded DNA genome of the virus associated with proteins is present inside the core.
8. Which type of capsid symmetry is present in T-even phages?
a) Rectangular
b) Spherical
c) Polygonal
d) Binal
View Answer
Explanation: The T-even phages are the T2, T4 and T6 phages. They have binal symmetry. The heads of their capsids resemble an icosahedron and the tail is helical. The icosahedral head contains the DNA genome. The tail contains a collar, a central hollow tube with sheath, and a complex baseplate.
9. The envelope proteins projecting out from the envelope surface are known as peplomers.
a) True
b) False
View Answer
Explanation: The envelope proteins are encoded by viral genes. They project out from the envelope surface as spikes. These are called peplomers. The spikes help in the attachment of virus particles to the host cell surface. The spikes can be used to identify viruses because they differ among different viruses.
10. Which of the following enzymes is present in the spikes of influenza virus?
a) Urease
b) Neuraminidase
c) Pepsin
d) Trypsin
View Answer
Explanation: Influenza virus is an enveloped virus. It has two types of spikes. Some of the spikes contain the enzyme neuraminidase. It helps in the release of mature virus particles from the host cells. The other spikes contain hemagglutinin proteins. They bind virus particles to red blood cells and cause the cells to clump together.
11. Which non glycosylated protein is present in the envelope of influenza virus?
a) Spike protein
b) Matrix protein
c) Nucleocapsid protein
d) Capsid protein
View Answer
Explanation: Most of the envelope proteins present in influenza virus are glycoproteins. These proteins have carbohydrate moieties attached to them. Only one non glycosylated protein is found in the envelope of influenza virus. It is the matrix protein. It is found on the inner surface of the envelope and helps in its stabilization.
12. Which structure is the intermediate in the spontaneous assembly of tobacco mosaic virus particles?
a) Spherical
b) Rectangular
c) Lock-washer
d) Polygonal
View Answer
Explanation: The lock-washer structure is the intermediate in the assembly of tobacco mosaic virus particles. They are very short helical structure. Their dimension is slightly more than two turns of a helix. These structures are produced from discs by slight changes in the conformation of protein subunits. The lock-washers assemble to form a helix of the virus particle.
13. Which of the following proteins are involved in the capsid assembly of polioviruses?
a) VP0, VP1, VP3
b) NP0, NP1, NP3
c) BP0, BP1, BP3
d) SP0, SP1, SP3
View Answer
Explanation: Poliovirus assembly begins from the three proteins VP0, VP1, and VP3. These proteins are produced by cleavage of the polypeptide P1. The three proteins associate with each other to produce a complex with sedimentation coefficient 5S. The association of these complexes form an empty 73S capsid.
14. Which sequences within the herpes simplex virus genome are required for its packaging?
a) Sp1 and sp2
b) Rc1 and rc2
c) Bac1 and bac2
d) Pac1 and pac2
View Answer
Explanation: The herpes simplex virus genome contains direct repeat sequences at the ends of the DNA which are known as the ‘a’ sequence. Each ‘a’ sequence contains two short regions, called pac1 and pac2. These regions are essential for the packaging of the herpes simplex virus particles.
15. Virus particles can carry enzymes within their capsids.
a) True
b) False
View Answer
Explanation: Viruses do not have true metabolism and they cannot reproduce outside living cells. But the virus particles can carry one or more enzymes within their capsids which are essential for the completion of their life cycles. For example, influenza virus particles have an RNA genome. So, they carry an enzyme that synthesizes RNA using an RNA template.
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