Question

What is not true about the retrovirus?
(a) DNA has no role in the life cycle
(b) There is a gene for RNA-dependent DNA Polymerase
(c) Genetic material is RNA
(d) They are causative agents for certain cancers.

Answer 1

Hint: Retroviruses are viruses that contain RNA as their genetic material. They insert their RNA into a host cell and incorporate themselves into the genome of the host. It requires more than one genetic material, and multiple enzymes for their infection.

Complete step-by-step answer:
- Retroviruses are viruses that have an RNA genome that it inserts into the DNA of the host genome, thus changing the genome of the cell.
- Retroviruses carry the RNA that encodes the reverse transcriptase enzyme, which produces DNA from its own RNA. The DNA is then integrated into the host genome through the enzyme integrase.
- The host cell then transcribes and translates the viral DNA as part of its own genome and produces the proteins required to assemble new copies of the virus. Hence, DNA is an integral of the life cycle of the retrovirus.
So, the correct answer is ‘DNA has no role in the life cycle’.

Additional Information:
- Reverse transcriptase is RNA-dependent DNA Polymerase, hence there is a gene for the enzyme in the virion.
- Retroviruses are causative agents for cancers in humans and animals such as sarcomas and leukemias.
- The RNA in retroviruses is single-stranded existing as a dimer in the viral envelope. They exist as three types - of retroviruses, lentiviruses, and spuma viruses.

Note:
- Most endogenous retroviruses are not pathogenic but the exogenous horizontally-transmitted viruses usually are.
- Examples of diseases in humans induced by or associated with horizontally-transmitted exogenous retroviruses are human adult T-cell leukemia, human tropic spastic paraparesis, and AIDS.
- The DNA formed after reverse transcription of RNA in the host is known as the provirus.