1. Viruses are microbes on the borderline of life. They can only be seen with an electron microscope. A virus particle consists of a few small fragments of genetic material (either DNA or RNA) contained in a protein coat. Just as a computer virus is simply code that must be run on a computer before it can do anything, so biological viruses cannot function until they get inside a living cell. The influenza virus is covered in surface protein molecules. E Viruses

2. Replication When a virus enters a living cell, it switches off the cell’s DNA and forces the cell to copy the virus’s genetic material and make new virus particles. Then the cell bursts (which kills it) and the virus particles are released to infect other cells.

3. Virus facts  Viruses do not respire, excrete or need food. The only life function they carry out is replication – after taking over a living cell to do it. Because they do not carry out all the functions of living things, viruses are not truly alive.  Viruses are very specific in their host cells: you get a cold in your nose, not your big toe.  Antibiotics will not kill viruses.  Viruses cannot be grown on an agar plate.  Virus particles can ‘survive’ on surfaces or even in food for days or weeks, before infecting a suitable living cell.

4. Viruses Each virus consists of genetic material (DNA or RNA) packaged in a tight fitting protein coat. Viruses are not truly alive because they do not respire, excrete or need food and use living cells to help them replicate. They replicate (multiply) by invading living cells and reprogramming them to copy the virus genetic material. The host cell is damaged in the process so viruses are always pathogens. Viruses cannot be grown on agar plates because they can only multiply in living organisms. 6E 1 Viral replication 6E 2 Virally speaking

5. Proceed to next chapter End of chapter