Why are retroviruses placed in a separate class of RNA viruses?
Correct answer: D. They use reverse transcriptase to make DNA from RNA
- A. They always infect animal cells only
- B. Their RNA acts directly as mRNA
- C. They lack protein coats
- D. They use reverse transcriptase to make DNA from RNA
Explanation
A retrovirus reverses the usual flow of information by copying its RNA genome into DNA, which integrase then inserts into the host chromosome as a provirus, and that integration is why HIV infection is lifelong. In other RNA viruses the genome often does act directly as messenger RNA, which is the contrast the second option draws. Retroviruses have perfectly ordinary capsids and envelopes.
This question appeared on the UHS MDCAT 2025 paper, which you can sit online with every answer explained.
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About Viruses
Viruses are acellular infectious particles made of genetic material enclosed by a protein capsid, sometimes with a lipid envelope. Their replication depends on a host cell and may follow lytic or lysogenic cycles, so viral structure and reproduction differ fundamentally from those of cellular organisms such as bacteria.
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