Explain how a retrovirus such as HIV integrates its genetic material into the host cell genome and discuss the consequences of this integration for the host cell.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
HIV carries the enzyme reverse transcriptase, which transcribes its single‑stranded RNA genome into a double‑stranded DNA copy during entry into the host cell. The newly formed viral DNA is transported into the nucleus where the viral enzyme integrase inserts it into the host cell’s chromosomal DNA, creating a provirus.
The provirus can remain latent, so the infected cell is not recognised by the immune system and antiretroviral drugs cannot eradicate these reservoirs. When the provirus is activated, host transcription machinery transcribes the viral genes, leading to synthesis of viral proteins and assembly of new virions. The infected cell may then be destroyed by cytotoxic T cells or, if integration disrupts a tumour‑suppressor gene or activates an oncogene, it can contribute to malignant transformation.
The provirus can remain latent, so the infected cell is not recognised by the immune system and antiretroviral drugs cannot eradicate these reservoirs. When the provirus is activated, host transcription machinery transcribes the viral genes, leading to synthesis of viral proteins and assembly of new virions. The infected cell may then be destroyed by cytotoxic T cells or, if integration disrupts a tumour‑suppressor gene or activates an oncogene, it can contribute to malignant transformation.
Examiner tips
- Use the terms reverse transcriptase, integrase, provirus, latent infection and malignant transformation
- Show the sequence: RNA → DNA → integration → latent/active
- Explain both immediate and long‑term cellular consequences
Common mistakes
- Confusing reverse transcriptase with integrase
- Forgetting that integration occurs in the nucleus
- Overlooking the latent reservoir or the oncogenic potential
Mark scheme (4 marks)
- HIV carries reverse transcriptase, which transcribes the viral RNA genome into DNA (reverse transcription).
- The viral DNA is transported into the nucleus and integrates into the host cell's chromosomal DNA using the viral enzyme integrase, forming a provirus.
- The provirus may remain latent (dormant) within the host cell, meaning the infection is not immediately cleared by the immune system / antiretroviral drugs cannot eliminate latent reservoirs.
- When the provirus is activated, host cell transcription machinery transcribes the viral genes, leading to production of new virions / the host cell may be destroyed or, if integration disrupts a tumour-suppressor gene or activates an oncogene, may lead to malignant transformation.
Key terms in this question
Related
- All IB DP Biology Higher Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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