1. Viruses AIDS Virus Polio Virus Bacteriophage Tobacco Mosaic Virus Influenza Virus Ebola Virus

2. Viruses are EVERYWHERE! They can be found pretty much anywhere – Computer keyboards, under your fingernails, in bird droppings They are extremely small! –They are smaller than the smallest bacteria Rhinovirus

3. What is a virus? Viruses are non-living particles They are considered to be non-living because they are not cells and the do not exhibit all the criteria for life – They don’t grow, develop, or carry out respiration – They cannot replicate without the help of living cells. A cell in which a virus replicates is called a host cell

4. How are viruses named? Because viruses are non-living they are not named the same way organisms are named Viruses can be named after: – the disease they cause (ex. Poliovirus, rabies virus) – the organ or tissue they infect (ex. adenovirus) Today, many viruses are given code numbers to distinguish among similar viruses that infect the same host (ex. T1, T = Type)

5. Viral Structure inner core of nucleic acid (RNA or DNA) outer coat made of protein called a capsid additional layer surrounding the capsid made of material similar to what is found in the plasma membrane called an envelope - only found in relatively large viruses - Contains genetic material which are instructions for making copies of the virus

6. The outer coat made of protein is called the… A.envelope B.capsid C.nucleic acid D.plasma membrane

7. Viral Structure

8. the arrangement of proteins in the capsid of the virus is very important! It can determine: 1. the shape of the virus 2. the type of host cell that can be infected 3. How the virus infects the cell The following slides are a few examples of different virus shapes.

9. Polyhedral Viruses Resemble small crystals Examples: –Papilloma virus (causes warts)

10. Helical Viruses long, narrow cylinders, with the genetic material spiraling down the center of a hollow protein tube Example: tobacco mosaic virus

11. Bacteriophages Viruses that infect bacteria Looks like a miniature lunar landing module DNA containing head, protein tail and protein tail fibers Example: –T4 virus infects E.coli

12. Enveloped Viruses Some viruses are enclosed in envelopes composed of lipids, carbohydrates and proteins Envelope proteins form spiky projections that help virus enter host cell Example: –HIV

13. Irregular Shaped Virus The Ebola Virus has a twisted worm-like form Causes massive internal bleeding in humans One of the most deadly viruses researchers have ever studied!

14. Attachment to a Host Cell Before a virus can replicate it must first attach to and then enter the host cell Attaching: - The virus attaches to a receptor site on the host cell’s plasma membrane The attachment protein on the virus can be on the tail fiber, in the capsid or in the envelope.

15. The virus in the picture is an example of what kind of virus? A.Envelope virus B.Polyhedral virus C.Bacteriophage D.Helical virus

16. Attachment is a specific process Each virus has a specifically shaped attachment protein therefore each virus can only attach to only a few kind of cells The recognition and attachment process is like two pieces of a puzzle fitting together Example: A T4 phage cannot infect a human cell, a plant cell or any other bacteria. It can only infect certain types of E. coli.

17. Entering the host cell Once attached to the host cell’s plasma membrane, the virus enters the cell and takes over its metabolism Viruses have 2 ways of getting into the host cell 1. Virus can inject its nucleic acids into a host cell 2. After attachment, the host cell’s plasma membrane surrounds the virus and produces a virus filled vacuole inside the host cell’s cytoplasm. Eventually, the virus bursts out and releases its nucleic acid into the cell

18. Viral Replication Cycles Lytic Cycle Lysogenic cycle - The virus uses the host cell’s energy and raw materials to make new viruses. - Typically, this cycle takes about 30 minutes and produces about 200 new viruses. - Does not destroy the cell at once, can continue for years - destroys the cell - The viral nucleic acid is integrated into the genetic material of the host cell and replicates with it for awhile before entering a lytic cycle

19. Lytic Cycle http://www.youtube.com/watch?v=wVkCyU5aeeU&feature=related

20. Lysogenic Cycle http://www.youtube.com/watch?v=_J9-xKitsd0

21. Lytic Cycles

22. This cycle can last for a long time A.lytic B.lysogenic

23. Provirus viral DNA that is integrated into the host cell’s chromosome - Formed during the lysogenic cycle Every time the host cell reproduces, the provirus is replicated along with the host cell’s chromosome At any time, the provirus can be activated and enter a lytic cycle  the virus can now replicate and kill the host cell

24. What causes a provirus to be activated? No one knows for sure! Some scientists believe that physcial stress (ie., sunburn) or emotional stress (ie., anxiety) may have an affect on activation

25. Many disease causing viruses may have lysogenic cycles Example: Cold sores caused by the herpes simplex I virus Even though cold sores heal, the herpes virus stays in your body as a provirus (lysogenic phase) When the provirus enters the lytic cycle another cold sore erupts

26. Release of virus How does the virus leave the host cell? Exocytosis  the host cell’s plasma membrane surrounds the virus creating a vacuole which then fuses with the plasma membrane and is released to the outside. Lysis  bursting of a cell

27. Proviruses are created during the A.Lytic cycle B.Lysogenic cycle

28. Retroviruses The retroviral DNA is then integrated into the host cell’s chromosome. A type of viral replication (the most complex) where a virus uses reverse transcriptase to make DNA from viral RNA Example: HIV (has RNA for it’s genetic material) How can RNA be integrated into a host cell’s chromosome which contains DNA?

29. Retroviruses - an enzyme inside the capsid which produces double stranded DNA from its RNA. The retrovirus makes DNA from its RNA using reverse transcriptase - this double stranded DNA is then integrated into the host’s chromosome and becomes a provirus.

30. Retroviruses

31. HIV Human Immunodeficiency Virus infects white blood cells - infected host cells still function normally because the viral genetic material is a provirus Because infected cells still function normally an infected person may not appear sick. - However, infected people can still transmit the virus in their bodily fluids.

32. HIV to AIDS People with HIV may not experience AIDS symptoms for a very long time. HIV turns into AIDS because over time more and more WBC’s get infected with the virus - people eventually lose WBC’s because the provirus enters a lytic cycle (which kills the WBC’s) WBC’s are vital to fighting infection. So people with AIDS lose their ability to fight infection.

33. Viruses and Cancer Retrovirus is one kind of virus that may cause some cancers. - the retrovirus can convert normal cells to tumor cells Examples: Papilloma Virus (causes warts) and the Hepatitis B Virus thought to cause liver cancer

34. Plant Viruses Tobacco Mosaic Virus was the first ever virus to be identified scientists know of more than 400 plant viruses Not all viral plant diseases are harmful This tulip was infected with a tobacco mosaic virus

35. All viruses are harmful to the host A.True B.False