Viral Diseases

For Edexcel GCSE Biology you need to know the details of three specific viral diseases: HIV, tobacco mosaic virus (TMV), and measles. You also need to understand why viral diseases are difficult to treat.

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How Viruses Cause Disease — A Recap

Viruses are not true living cells. They are tiny particles consisting of a piece of genetic material (DNA or RNA) surrounded by a protein coat (capsid). Some viruses also have a lipid envelope.

How they work:

1. The virus attaches to a specific receptor on the host cell surface
2. It injects its genetic material (or enters the cell whole)
3. The viral genetic material takes over the cell's machinery
4. The cell is forced to produce many copies of the virus
5. The host cell fills with new virus particles and eventually bursts (lysis)
6. New viruses are released to infect neighbouring cells

This destruction of host cells causes the symptoms of viral disease.

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1. HIV (Human Immunodeficiency Virus)

What It Is