Virus

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

Measles is a disease caused by a group of viruses called Morbilliviruses. It can cause a rash, blindness and brain damage.

AIDS is a disease caused by a virus called HIV. The symptoms are a weakening of the immune system which leads to other infections.

Tobacco Mosaic Virus is a virus which causes Tomato Plants and Tobacco Plants to grow slowly.