Name Date Class. Viral Replication

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1 EXPLORATION Viruses are very successful at invading the cells of organisms. A virus first becomes attached securely to the outside of a host cell. Then, some viruses inject their nucleic acid into the cell and leave their coat outside the cell; other viruses still have their coats when they enter the cell. Once many types of viruses are inside a host cell, they insert viral genes into the host DNA. The viral genes direct replication, causing the cell to make many new copies of viral genes. At the same time, the cell s protein synthesis machinery is directed to make many new viral coats and enzymes. The virus particles are assembled, and the new viruses escape from the cell either by exocytosis or by bursting out of the cell. OBJECTIVES Trace the steps of viral replication in cells. Describe the steps of viral replication. Construct an analogy for viral replication in cells. MATERIALS glue scissors photocopy of model viruses and viral parts goggles PROCEDURE 1. Study Figures 1 and 2 so that you become familiar with viral structures and with the models of viral structures that you will use in this Exploration. 2. The teacher will give you a photocopy of drawings that represent viruses and viral parts. Cut out the drawings. 3. Each drawing corresponds to one of the numbered steps of viral replication listed at the end of the Procedure. Using Figure 2 as a key, label the tab on each drawing with the number of the step of viral replication that it represents. 4. Examine Figure 3 under Data and Observations. The diagram summarizes the steps of viral replication within a cell. The location of each step is labeled. Match each cutout drawing with the correct label. Then copy the numbers from the drawings onto the appropriate spaces provided in the diagram. 5. Place each drawing over its corresponding label in Figure 3. When complete, have your diagram checked by the teacher for accuracy. 6. Once the drawings are in their proper positions on the diagram, glue them in place. LABORATORY MANUAL CHAPTER 18 BIOLOGY: The Dynamics of Life 125

2 PROCEDURE continued Figure 1 Figure 2 Viral structure Key for cutout drawings Steps of 1. The virus attaches to the host s cell membrane. 2. The virus enters the cell. 3. The protein coat of the virus is removed. 4. Viral genes are activated. 5. a. The activated genes direct replication of viral genes. b. The activated genes direct protein synthesis to make new viral coats and enzymes. 6. a. New viral genes are completed. b. New viral coats are completed. 7. The new viruses are assembled. Genes are inserted into the protein coats. 8. The new viruses are released from the cell. 126 CHAPTER 18 BIOLOGY: The Dynamics of Life LABORATORY MANUAL

3 DATA AND OBSERVATIONS Figure 3 Life Cycle of a Virus LABORATORY MANUAL CHAPTER 18 BIOLOGY: The Dynamics of Life 127

4 ANALYSIS 1. In what way is viral replication different from cell reproduction? 2. Examine your completed diagram of viral replication. What two processes are directed by viral genes that are activated inside the host cell? 3. Describe the stage that occurs before viruses are released from the cell. 4. If you were a scientist developing a drug that would block viral replication, which steps would you choose to block? Explain. 5. The analogy you are working with in this Exploration compares viral replication with the making of a product in a factory. In what ways does the analogy not hold true? FURTHER EXPLORATIONS 1. Read the article Viruses Have Many Ways to Be Unwelcome Guests, by Michael Balter, Science, April 10, 1998, pp Write an essay that explains the different ways viruses invade host cells and replicate. 2. Use the library to research retroviruses. Determine how their replication differs from that shown in this Exploration. Change the factory analogy to account for these differences. 128 CHAPTER 18 BIOLOGY: The Dynamics of Life LABORATORY MANUAL

5 Teacher Guide EXPLORATION Objectives Trace the steps of viral replication in cells. Describe each step of viral replication. Construct an analogy for viral replication in cells. Process Skills observe, recognize and use spatial relationships, formulate models Time Allotment 1 class period 4. Answers will vary. One could block attachment of the virus, block viral coat removal so cell machinery is not taken over, block production of either viral coats or viral genes so new viruses could not be formed, or block the release of the viruses. 5. Answers will vary. Viral replication involves the use of a virus to make more viruses. When a product is made in a factory, it isn t made from an existing product of the same kind. Also, factories usually aren t destroyed making products. Figure 3 Materials glue (15 bottles) scissors (15) photocopies of model viruses and viral parts (15) goggles (30) Preparation Make a photocopy of page T33 for each group. Teaching the Have students work in pairs. Emphasize the use of the key in Figure 2 before beginning. Encourage students to go on to the next step of viral replication if they can t figure out which cutout matches a particular number. Troubleshooting: If students are having problems, reinforce the idea that each cutout matches a number in the steps of viral replication and that it also matches a label on the cell diagram. The sequence of steps goes from top to bottom on the cell diagram. Data and Observations See Figure 3. Analysis 1. Cells reproduce on their own by mitosis or binary fission. In contrast, viruses must infect living cells and use the cells machinery in order to replicate. 2. New viral genes and new viral coats are produced. 3. The new viral genes are inserted into the new viral coats. LABORATORY MANUAL ANSWER PAGES BIOLOGY: The Dynamics of Life 35T