Retroviral life cycle — Retroviruses replicate via which type of nucleic acid intermediate inside infected cells?

Introduction:
Retroviruses package RNA genomes but integrate into host chromosomes. This question targets the central dogma reversal step that defines retroviral replication.

Given Data / Assumptions:

• Retroviruses (e.g., HIV) carry an RNA genome.
• They encode reverse transcriptase.
• Integration into host DNA is required for productive infection.

Concept / Approach:
Reverse transcriptase synthesizes complementary DNA (cDNA) from the viral RNA template, yielding a double-stranded DNA intermediate. This proviral DNA integrates into host chromosomal DNA via integrase. Transcription by host RNA polymerase II then produces viral mRNAs and genomic RNA for assembly.

Step-by-Step Solution:

Verification / Alternative check:
Antiretroviral drugs targeting reverse transcriptase (e.g., NRTIs, NNRTIs) block DNA intermediate formation, validating its essential role in the life cycle.

Why Other Options Are Wrong:

• RNA/mRNA alone: these are templates, not the integrated intermediate.
• rDNA: refers to ribosomal DNA repeats, unrelated to retroviral replication.
• Protein–RNA hybrid: not the key replicative intermediate.

Common Pitfalls:
Assuming RNA viruses always replicate only via RNA intermediates; retroviruses are the classic exception due to reverse transcription.

Final Answer:
DNA.