1. Viruses Chapter 19-2

2. What is a virus? Viruses- microscopic particles that invade cells and destroy them. A virus is NOT a cell. Has genetic material in a protein coat. Herpes Simplex Influenza Virus H5N1 (avian influenza)

3. What Is a Virus? Head Tail sheath DNA T4 Bacteriophage Tobacco Mosaic Virus Influenza Virus RNA Membrane envelope Tail fiber RNA Capsid proteins Capsid Surface proteins

5. Genetic Material Depending on the virus type, genetic material may consist of: - DNA Or - RNA (retrovirus)

6. Protein Coat - Called a capsid - Encloses the viral genome - Built of a large number of protein subunits called capsomeres, but with limited diversity.

7. The most complex capsids are found in viruses that infect bacteria, called bacteriophages or phages. The virus makes the host cell into a virus making factory that attaches the phage to the host and injects the prophage DNA inside.

8. How does a virus infect a cell? Viruses are obligate intracellular parasites. –The virus makes the host cell into a “virus making factory”. –They can reproduce only within a host cell by inserting their genetic material into the host.

9. Viral infections Viruses identify host cells by a “lock-and- key” fit between glycoproteins on the outside of virus and specific receptor molecules on the host’s surface. This helps the virus invade the host cell.

10. Viral Infection After entering the cell and replicating genetic material, one of two pathways might be taken: –Lytic Cycle –new viruses causes the cell to burst (or “lyses”), releasing newly made viruses that will infect other cells –Lysogenic Cycle – Viral DNA becomes part of the cell’s DNA and then replicates along with the cell. (does NOT cause the cell to burst right away)

12. HIV (Human Immunodeficiency Virus) HIV attacks helper T-Cells called lymphocytes –Helper T-cells fight infection AIDS occurs when the helper T cells are almost all killed. - can develop from HIV within a few months or take as long as 10 years.

14. Infection; Immune system eliminates most of HIV Symptoms, such as swollen lymph nodes, are few Loss of immune function more apparent; appearance of characteristic diseases such as yeast infections Almost total loss of cellular immunity; AIDS Relative HIV concentration T cell concentration Section 40-3 Stages of HIV Infection Years

15. Are viral infections curable? Viral infections must run their course typically. Some prescription medicines can shorten the length of illness by destroying viruses. –The active substance in Tamiflu acts specifically on the flu virus, blocking some of the enzymes on its surface known as neuramidases (the glycoprotein that helps flu virus infect upper respiratory cells).

16. Are viral infections preventable? Yes! –Good hygiene is your best defense. –Vaccines These are injections that help your immune system build immunity. The vaccine is made of weakened or destroyed viruses so that your body can make antibodies. When your body comes into contact with the real thing, your immune system antibodies recognize and destroy the viruses immediately!

17. Review

18. DRAW AND LABEL THE VIRUS AND BACTERIUM IN THE FOLLOWING T- CHART. LABEL THE STRUCTURES. UNDER EACH PICTURE, DEFINE ALL THE LABELED TERMS. Bacteria Virus