Question

Which of the following is NOT a criterion for classifying viruses?

a)Type of organism the virus infects

b) Method of viral replication

c) Type of nucleic acid in viral genome

d) Envelope structure or composition

e) All of the above are used

Answer 1

Viruses are nucleoprotein complexes i.e. they are made of a genomic core of either RNA or DNA surrounded by a protein coat/envelope. Some viruses also have an additional lipid covering.

There are several ways of classifying viruses.

1. Type of the host organism: Based on the organism, viruses infect, they can be classified as plant viruses, animal viruses, bacteriophages, etc. The viruses are host-specific and hence can infect only a specific host.

2. Method of viral replication: Based on the replication mode used, the viruses can be classified as lytic or lysogenic viruses. Lytic viruses infect the host, replicate, form virions and start a new cycle. Lysogenic viruses infect the host, get integrated into the genome and stay dormant and replicate along with the host genome.

3. Type of nucleic acid in the genome: Based on the nature of the nucleic acid present, viruses can be classified as DNA viruses or RNA viruses. Viruses can have either DNA or RNA but never both. Each of these is further classified based on whether the DNA or RNA is single-stranded or double-stranded.

4. Envelope structure: The protein envelope is highly symmetrical in viruses due to the repeating protein units that make the envelope. Based on the geometry as observed under an electron microscope, viruses can be classified as icosahedral, octahedral and so on.

Hence the correct answer for the question is E) All of the above.