Exercise: Viruses: Alive or not?!? A special case.

A virus consists of DNA (or a related molecule, RNA) wrapped with a protein "coat" and sometimes an outer envelope borrowed from its host cell.

The coat can consist of hundreds of proteins arranged in symmetrical, complex patterns.

Viruses are much smaller than even a bacterial cell, and can only be seen with an electron microscope.

Viruses do not have organelles, cytoplasm, or any of the internal structures of cells.

Viruses reproduce, but are unable to reproduce on their own. To reproduce, a virus must infect a host cell and take over the host's cellular machinery, instructing it to make more virus particles. Viruses are thus parasites of other cells - that is the only way they can reproduce.

There is more about viruses on pages 317-319 of your text.

Questions to discuss with a partner - Introduce yourself!

1. In what way(s) of the 5 we discussed could viruses said to be "alive"?

2. What components do viruses lack that are shared by living organisms?

3. Are viruses "alive" or not?