Which term describes the complete set of steps from attachment to egress?
Answer: C
The multiplication or replication cycle covers the whole sequence in a single infected cell. The eclipse is one interval within it, while a plaque assay and cytopathic effect are ways of observing that it has happened.
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Progeny virions accumulate at exponential rates during
Answer: D
Correct answer: maturation
Maturation is the assembly of the synthesised components into complete particles, so it is during this phase that infectious virus reappears in the cell and accumulates rapidly. Before it lies the eclipse phase, during which the genome and proteins are being made but no infectious particle can be recovered - which is why the yield curve stays flat and then rises steeply.
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The first step in the replication of a virus with the reverse transcriptase deals with the synthesis of
GATE Life Sciences - 2012,
Answer: C
The first step is synthesis of a complementary strand of DNA.
In a retrovirus such as HIV, reverse transcriptase first uses the viral RNA genome as a template to make a complementary DNA strand, giving an RNA-DNA hybrid. Its RNase H activity then degrades the RNA, and the enzyme makes the second DNA strand, producing double-stranded DNA that is integrated into the host genome.
Double-stranded DNA is the end product of reverse transcription, not its first step, and making a complementary RNA strand or double-stranded RNA is RNA-dependent RNA synthesis, which reverse transcriptase does not perform.
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Monkey pox is caused by a
GATE Life Sciences - 2023,
Answer: A
Monkeypox is caused by a double-stranded DNA virus.
The monkeypox (mpox) virus belongs to the genus Orthopoxvirus of the family Poxviridae, the same genus as the variola (smallpox) and vaccinia viruses. Poxviruses have large linear double-stranded DNA genomes of about 200 kb and, unusually for DNA viruses, replicate in the cytoplasm.
Single-stranded DNA viruses such as parvoviruses, double-stranded RNA viruses such as rotaviruses, and single-stranded RNA viruses such as influenza or SARS-CoV-2 belong to entirely different families.
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Correctly match the viruses listed in Column I with the nature of their corresponding genetic materials listed in Column II.
| Column I | Column II |
|---|---|
| P. Bacteriophage lambda | i. dsDNA |
| Q. Bacteriophage M13 | ii. ssDNA |
| R. Coronavirus | iii. ssRNA |
| S. Reovirus | iv. dsRNA |
GATE Life Sciences - 2025,
Answer: C
The correct match is P - i; Q - ii; R - iii; S - iv.
The other options give M13 RNA or double-stranded DNA, or make reovirus a DNA virus, each contradicting these well-known genome types.
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The genome of which one of the following viruses encodes reverse transcriptase?
GATE Life Sciences - 2026,
Answer: A
The virus whose genome encodes reverse transcriptase is the human immunodeficiency virus.
HIV is a retrovirus. Its pol gene encodes reverse transcriptase, which copies the single-stranded RNA genome into double-stranded DNA; integrase then inserts that DNA into the host chromosome as a provirus.
Influenza and rabies viruses have negative-sense RNA genomes and carry an RNA-dependent RNA polymerase. Poliovirus has a positive-sense RNA genome that encodes its own RNA-dependent RNA polymerase. None of the three makes DNA from its RNA.
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Viral capsids are made up of morphological subunits called capsomeres. One of the common capsomeres is icosahedral. The icosahedron is a regular polyhedron with
IIT JAM - 2018,
Answer: B
An icosahedron has 20 triangular facets and 12 vertices.
The regular icosahedron is a solid of 20 equilateral triangular faces, 30 edges and 12 vertices, with five faces meeting at each vertex. Euler's formula confirms it: \(V - E + F = 12 - 30 + 20 = 2\).
Many viruses, such as adenovirus, build their capsids on this pattern. The options with 16 facets or 16 vertices do not describe any regular polyhedron, and Euler's formula fails for them with 30 edges.
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Which one of the following animal viruses contains double stranded RNA as genetic material?
IIT JAM - 2026,
Answer: D
The virus with a double stranded RNA genome is Reovirus.
Reoviruses (family Reoviridae, which also includes rotavirus, the main cause of severe infant diarrhoea) carry a segmented genome of 10-12 pieces of double stranded RNA, packed inside a double-layered protein capsid together with their own RNA polymerase.
The other three have single stranded RNA. Influenza virus has a segmented negative-sense single stranded genome. Rous sarcoma virus is a retrovirus with two copies of positive-sense single stranded RNA, copied into DNA by reverse transcriptase. Poliovirus is a picornavirus with one positive-sense single stranded RNA.
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