Explain how a virus with a lipid envelope acquires that envelope and why its presence affects the ability of the immune system to recognise and neutralise the virus.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Enveloped viruses acquire their lipid envelope from the host cell membrane (plasma membrane, nuclear envelope or ER) when they bud out of the cell.
During budding, viral glycoproteins encoded by the viral genome are inserted into the host membrane and become embedded in the budding envelope.
Because the envelope is host‑derived, the lipid bilayer is chemically similar to the cell’s own membranes, so the immune system may not recognise it as foreign. This reduces detection by innate immunity.
Neutralisation therefore depends on antibodies recognising the viral glycoproteins on the envelope surface. If the glycoproteins are altered (antigenic variation) or present in low numbers, antibody binding is reduced and the virus evades neutralisation.
During budding, viral glycoproteins encoded by the viral genome are inserted into the host membrane and become embedded in the budding envelope.
Because the envelope is host‑derived, the lipid bilayer is chemically similar to the cell’s own membranes, so the immune system may not recognise it as foreign. This reduces detection by innate immunity.
Neutralisation therefore depends on antibodies recognising the viral glycoproteins on the envelope surface. If the glycoproteins are altered (antigenic variation) or present in low numbers, antibody binding is reduced and the virus evades neutralisation.
Examiner tips
- Mention the specific host membrane source (plasma, nuclear, ER) to gain full marks. Show that viral glycoproteins are inserted before budding. Explain that the envelope is host‑derived and why this hinders immune recognition. State that neutralisation requires antibodies to target envelope glycoproteins and that variation reduces this.
- common_mistakes
- :
- Saying the envelope comes from the virus itself rather than the host cell. Forgetting that the envelope is host‑derived and therefore less immunogenic. Not linking the presence of the envelope to the need for antibodies to target viral glycoproteins.
Mark scheme (4 marks)
- Enveloped viruses acquire their lipid envelope from the host cell's membrane (plasma membrane or nuclear envelope / endoplasmic reticulum membrane) during budding.
- Viral glycoproteins (encoded by the viral genome) are inserted into the host membrane before budding, and these become embedded in the envelope.
- Because the envelope's lipid bilayer is host-derived, the immune system may not recognise it as foreign / it resembles the host's own membranes, reducing immune detection.
- Antibodies (and other immune effectors) must target the viral glycoproteins on the envelope surface to neutralise the virus; if these glycoproteins change (antigenic variation) or are sparse, neutralisation is less effective.
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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