IMAT 2021 Q23 [Viruses & Nucleic Acids]

Which of the following types of nucleic acid is/are found in viruses ?

  1. single-stranded DNA
  2. double stranded DNA
  3. RNA

A. 1, 2 and 3
B. 1 and 2 only
C. 2 only
D. 1 and 3 only
E. 2 and 3 only

The correct is A : all of them.

Every virus has the same basic structure :

  1. a capsid
  2. viral genome
  3. envelope protein

Viral genome

The viral genome can either be DNA (double or single stranded) or RNA.

  • Examples of viruses that contain double stranded DNA are Herpesviruses (like HSV).

  • Examples of viruses that contain single stranded DNA are Parvoviruses (like the canine parvovirus, that causes digestive problems among others).

  • Examples of viruses that contain RNA are retroviruses (like HIV) : it uses the host’s cells to convert RNA into DNA, thanks to its reverse transcriptase.

Envelope protein

The envelope is an external structure that: contains the capsid. It has a role in the process of viral infection, and to protect the virus against the immune system. It is made of a lipidic membrane and glycoproteins.


The capsid is the structure that contains the genetic material of the virus, either DNA or RNA. It is made of several protein units. Its purposes are to serve as a protector of the genome, to allow the virus’ attachment to host cells and to ensure its penetration.