Station 4

1. Reporting Category 1 Cell Structure and Function Station 4 Viruses: Structure, Replication, and Disease

2. Essential Question Why is it necessary for a virus to invade a living cell to make copies of itself? Viruses do not have the capability to reproduce as living cells do. A virus must make use of a cell’s functions, parts, and enzymes in order to replicate itself.

3. Pre-Review Question • Is a virus considered to be alive? NO

4. Pre-Review Question • Which of the following do viruses and cells have in common? A. They both contain nucleic acids. B. They both have mitochondria. C. They can both be multicellular. D. They both have a capsid.

5. Lab Activities • You will now go to the lab and complete the activities for today’s topics.

6. 1. Locate the Structures of Viruses and Cells sheet at this station. Carefully examine the structures of the plant cell, animal cell, bacteriophage virus, and influenza virus. Draw the chart in your journal and fill it in. Structures found in a virus Both Structures found in a cell

7. 1. Locate the Structures of Viruses and Cells sheet at this station. Carefully examine the structures of the plant cell, animal cell, bacteriophage virus, and influenza virus. Draw the chart in your journal and fill it in. Structures found in a virus Protein Coat Tail (bacteriophage) Fibers Capsid Membrane envelope Both Nucleic Acid Structures found in a cell Vesicles cytoplasm Nucleus nucleolus Vacuoles Cell wall Centrosomes lysosomes Cell membranes Mitochondria Golgi complex Endoplasmic reticulum Chloroplasts (plants)

8. 2. Discuss with your partner:Scientists consider viruses to be nonliving. Based on the information you used to fill in the Venn diagram, would you support or refute this statement? Explain your position. According to the information in the Venn diagram, the only structure or component that a virus and a cell have in common is nucleic acid. The virus lacks all the other cellular structures, and without them, it cannot exist, thrive, and reproduce on its own. Thus unlike living cells, viruses do not reproduce: They replicate by controlling the DNA and protein production of a living cell.

9. 3. Discuss with your partner:Some disinfectants claim that they are effective at killing viruses. Does your knowledge of the structures and functions of a virus support or refutethis claim? Explain your position. Viruses do not exhibit characteristics of a living organism and are therefore considered to be nonliving. The product’s claim that it “kills” viruses is questionable, since only living things can be killed. A virus’ structure may be destroyed, rendering the virus incapable of entering a living cell to make copies of itself, but it is inaccurate to say a virus can be killed.

10. 4. Locate the Lytic Infection Cycle sheet and the envelope labeled Lytic Infection cards. Place the cards in the proper sequence on the Lytic Infection Cycle sheet to represent how a virus can infect a living cell and cause the cell to replicate the virus. • Draw, label and describe only the last stage of the lytic cycle and the last stage of the lysogenic cycle.

11. 5. Discuss with your partner:Not all viruses replicate through lytic infection. Some viruses replicate by another method, called lysogenic infection. In this method, as in lytic infection, the virus injects DNA into the host cell, and the virus DNA combines with the DNA of the host cell. This may not cause any damage to the cell for weeks, months, or years. Then the virus DNA begins a process of replication similar to that found in lytic infection. The human immunodeficiency virus (HIV) replicates by the lysogenic infection method, attacking the cells of our immune system. Why do you think a person infected with HIV has difficulty fighting infections?See next slide for answer.

12. 5 cont.HIV replicates by lysogenic infection, meaning that the virus’s DNA and the immune system cell’s DNA combine. Once the virus has replicated, it breaks out of the host cell by a process called lysis. The newly replicated viruses repeat the process with other immune system cells, destroying them and eventually weakening the immune system to the point that it is unable to fight off infections.

13. 6. Discuss with your partner:Locate the model of HIV at this station. Carefully examine the model without removing any of its parts. If a scientist tried to use this model to understand the structure and function of HIV, what limitations would he/she have? Answers may vary. Possible responses listed below. The model may not represent all of the virus’s structures. There is no means to test the model in a laboratory setting. It is not possible to see how the model behaves with a host cell.

14. I need to remember……… • Viruses lack the cell structures necessary for reproduction. • Viruses are considered nonliving. • Viruses can replicate by two methods—lytic infection and lysogenic infection. • Lysogenic infections occur when the nuclear material of the virus combines with the DNA of a cell before replication of the virus begins. • Viruses and cells have one structure in common, nucleic acids. • HIV is a virus that infects and destroys immune system cells.

15. Post Review Questions • Can a virus attack any cell in your body? No, it only attacks cells with specific protein markers.

16. Post Review Questions In which cycle can the virus remain dormant for a long time? Lytic or Lysogenic

17. Post Review Questions Name the type of cell attacked by the following viruses. HIV - Hepatitis C – Flu – T Cells Liver Cells Epithelial cells of the respiratory system