Contents
Key Stage 4
Meaning
A virus is a type pathogen that can infect individual cells in an organism.
About Viruses
- Viruses are made from a strand of DNA or RNA and a protein sheath.
- Viruses cannot reproduce outside a host cell so they are not considered to be alive.
- When a virus comes in contact with a target cell it attaches itself to the cell membrane and then injects its DNA (or RNA) into the cell. Once this is done the DNA causes the cell to start making copies of the virus. When millions of copies have been made they burst out, killing the cell. These millions of viruses can then go on to infect other cells.
- Different viruses can only attach themselves to certain types of cell, so they can all have very different effects on the organism depending on which type of cell they infect.
Examples
- The measles virus causes causes a rash, blindness and brain damage.
- HIV causes a disease called AIDS which has the symptoms of a weakened immune system which leads to other infections.
- Tobacco Mosaic Virus is a virus which causes Tomato Plants and Tobacco Plants to grow slowly.