Viruses

1. Viruses

2. What are Viruses? • Viruses are particles of nucleic acid, protein, and in some cases lipids. • All viruses enter living cells • According to science, viruses first developed from living cells.

3. Discovery! A plant disease in the 1800’s caused tobacco leaves to produce pale spots. A kind of juice containing particles was the cause of this disease. In 1897, MartinusBeijerinck classified the particles as viruses. The Latin word meaning poison.

4. Structure of a Virus • A typical virus is made up of a core containing DNA or RNA with a protein coat instead of a cell wall. • The protein coat or capsid allows the virus to enter a cell. • The capsid is what tricks the cell to let the virus in.

5. T4 Bacteriophage Tobacco Mosaic Virus Influenza Virus

6. Viral Infection • Viruses are very specific to the cells they infect. e.g.animal virus to animal; plant virus to plant; bacterial virus to bacteria. • Viruses that infect bacteria are called bacteriophages. e.g.T4 and Lambda • There are 2 different types of viral infection: Lytic and Lysogenic. They have their own cycles which are interchangeable.

8. Lytic Cycle Explained • Virus or bacteriophage attaches to the cell. • The virus then injects its own DNA into the cell creating RNA which takes over the infected cell. • The virus then causes the infected cell to make copies of the itself. • When the copies of the virus have been made they lyse or break out of the cell wall. • The viruses then go to infect other cells.

10. Lysogenic Cycle Explained • After the virus’ DNA is injected, it is attached to the infected cells DNA. • The virus’ DNA can replicate through cell division many times. • Then the virus can actually separate its DNA from the infected cells DNA. • From this point, the Lysogenic Cycle can jump to the Lytic Cycle but only in certain situations.

12. Lysogenic to Lytic • After the viruses DNA separates from the cells DNA, the lysogenic cycle can jump to the lytic cycle. • Under certain conditions can the lysogenic cycle transition to the lytic cycle.

13. Human Viruses • Examples of human viruses are: Polio, measles, HIV, influenza, yellow fever, and more. • The virus attacks some areas of the human cell causing the symptoms of the virus. • Most viruses follow the lytic and lysogenic cycles of bacteriophages

14. Vaccines • A vaccine is a preparation of weakened or killed virus or viral protein. • The vaccine stimulates the immune system and may result in permanent immunity of the disease. • Vaccines should be given before an infection and not after.

15. Oncogenic Viruses • Oncogenic viruses cause a disruption among the control of cell growth and division. • Oncogenic viruses cause cancer. • These viruses only cause cancer in animals and humans.

17. Retroviruses • Retroviruses are viruses that have RNA as their genetic information. • Retroviruses have their genetic information copied backward. RNA to DNA instead of DNA to RNA. e.g. HIV

18. Prions • In 1972 an American scientist names Stanley Prusiner discovered prions. • Prions are particles that contain no DNA or RNA only protein particles. • However, these protein particles are infectious and cause several diseases in humans and animals. • e.g. Mad cow Disease

19. Viruses: Are they “Alive?” • According to science, viruses are not “alive.” • Viruses are not cells and cannot reproduce on its own. • Viruses, on the other hand, make copies of themselves, regulate gene expression, and evolve only when infecting a living cell.

20. What do you think? Would you consider a virus “alive?” Share your opinion.