Question

Explain how the single-stranded RNA of viruses give rise to double-stranded DNA.

Answer 1

The conversion of single-stranded viral RNA into double-stranded DNA is called reverse transcription and is carried out by the viral enzyme reverse transcriptase.

The process follows these steps:

1. First Strand Synthesis: After entering the host cell, the enzyme uses the viral single-stranded RNA as a template to synthesise a complementary DNA strand, forming an RNA-DNA hybrid.
2. RNA Degradation: An associated enzyme activity (RNase H) degrades the original viral RNA strand within the hybrid, leaving only the newly synthesised single DNA strand.
3. Second Strand Synthesis: The reverse transcriptase then uses this single DNA strand as a template to synthesise a second, complementary DNA strand.
4. Result: This results in a stable double-stranded DNA molecule, which can then be integrated into the host cell's genome by another enzyme called integrase.