Virus structures vary in genome chemistry and arrangement, capsid geometry, envelope presence, size, shape, and specialized components suited to different replication strategies.
Coverage 2013–2025 · Updated 15 Jul 2026
Viruses vary in genome type, capsid shape and whether they carry a host-derived membrane envelope.
| Example | Genome | Outer structure | Distinctive form |
|---|---|---|---|
| Bacteriophage lambda | Double-stranded DNA | Non-enveloped protein capsid with tail | Complex head-tail particle that infects E. coli |
| Coronavirus | Single-stranded RNA | Enveloped with projecting spike proteins | Roughly spherical enveloped particle |
| HIV | Two copies of single-stranded RNA | Enveloped | Conical capsid inside the envelope |
Across viruses, genetic material may be DNA or RNA and single- or double-stranded. Capsids can adopt different geometries, and envelopes are present in some lineages but absent in others.
An envelope can aid fusion with a host membrane but is more easily disrupted by detergents or drying than a protein capsid.
Shape alone does not determine host range or identify a species; receptor matching and replication compatibility also matter.
This objective is assessed through structured response, commonly using Outline / State / Describe.
Outline / State / Describe
Build the answer around this relationship: Viral genomes may be DNA or RNA and may be single- or double-stranded.
Claiming that a virus contains both DNA and RNA instead of one type of nucleic acid genome.
Representative question
Describe, with examples, the diversity of structure in viruses.
A strong HL virus answer usually combines two moves: define the boundary, then explain the mechanism or consequence. Viruses have DNA or RNA plus a capsid but lack the machinery for independent metabolism. Their diversity is described by genome, capsid, and envelope. Lambda phage lets you contrast lytic takeover with lysogenic integration. Origin questions require competing hypotheses and polyphyly. Evolution questions require mutation, recombination, short cycles, large populations, and examples such as influenza or HIV.
