Viral Diseases (HIV, Measles, TMV)

This lesson covers the three viral diseases named on the AQA GCSE Combined Science Trilogy specification (8464): measles, HIV and tobacco mosaic virus (TMV). You need to know the symptoms, how each is transmitted, and how it can be treated or prevented.

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How Viruses Cause Disease — Recap

Viruses are not true living cells. They consist of a strand of genetic material (DNA or RNA) surrounded by a protein coat called a capsid. Because they have no cellular machinery, they must:

1. Attach to a host cell and inject their genetic material
2. Use the host cell's enzymes and ribosomes to replicate viral DNA/RNA and make new viral proteins
3. Assemble many new virus particles inside the host cell
4. The host cell bursts (lysis), releasing hundreds of new viruses

graph LR
    A[Virus attaches to host cell] --> B[Injects genetic material]
    B --> C[Host cell replicates viral DNA/RNA]
    C --> D[New virus particles assembled]
    D --> E[Host cell bursts — lysis]
    E --> F[New viruses infect more cells]
    F --> A