Explain how RNA viruses such as HIV overcome the challenge of replicating their genetic material inside a host cell.

IB DP Biology Higher Level (2023 syllabus) — A2.3 Viruses (HL only) · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

HIV is a retrovirus with a single-stranded RNA genome. Unlike DNA viruses, retroviruses must convert their genetic information into a form compatible with the host cell's molecular machinery before integration and replication can occur.

Model answer (4 marks)

HIV carries the enzyme reverse transcriptase, which transcribes its single‑stranded RNA genome into complementary DNA (cDNA). The cDNA is then converted into double‑stranded DNA (dsDNA) – reverse transcriptase first degrades the RNA strand (RNase H activity) and then synthesises the second DNA strand. Viral integrase inserts this dsDNA into the host chromosome, forming a provirus. The host cell’s RNA polymerase then transcribes the proviral DNA, producing viral mRNA and new viral RNA genomes, thereby using the host’s replication machinery.

Examiner tips

  • Mention reverse transcriptase and integrase explicitly
  • Show the step of RNA degradation and second‑strand synthesis
  • Explain that host RNA polymerase transcribes the provirus
  • Keep answer concise and use correct terminology

Common mistakes

  • Confusing reverse transcriptase with DNA polymerase
  • Omitting the RNase H step or second‑strand synthesis
  • Failing to state that the provirus is integrated into the host genome

Mark scheme (4 marks)

  1. HIV carries the enzyme reverse transcriptase, which transcribes the viral RNA genome into complementary DNA (cDNA / DNA).
  2. The single-stranded DNA is converted into double-stranded DNA (dsDNA) by reverse transcriptase (or RNase H activity degrading the RNA strand followed by second-strand synthesis).
  3. The viral enzyme integrase inserts the double-stranded viral DNA into the host cell's chromosome, forming a provirus.
  4. The host cell's own RNA polymerase transcribes the proviral DNA, producing viral mRNA and new viral RNA genomes, thereby exploiting the host's replication machinery.

Related

More Viruses (HL only) questions

▶ Try answering this question with AI marking (free) →