16 HIV/AIDS Infection and Cell Organelles ALTHOUGH MANY OF their characteristics are similar to those of cells, viruses

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1 16 HIV/AIDS Infection and Cell Organelles ALTHOUGH MANY OF their characteristics are similar to those of cells, viruses are not cells. They contain genetic material and a few proteins, but they do not conduct cellular functions. For example, a virus can neither metabolize nutrients needed to grow and to develop essential structures, nor can it reproduce on its own. To reproduce, a virus must infect a living host cell. Viruses are specific to their hosts. Some infect one kind of animal, while others infect plants or even bacteria. Once it is inside the host cell, the virus takes over the cell s structures, enzymes, and organelles that will enable it to reproduce. Challenge How does HIV take over a cell s structures and organelles during infection and use them to reproduce? MATERIALS FOR EACH PAIR OF STUDENTS set of 13 Cell Structures and Organelles Cards colored pencils FOR EACH STUDENT Student Sheet 16.1, Scientific Diagram of HIV Infection Student Sheet 2.1, Disease Information, from Activity 2 sticky notes An electron microscope image of HIV virus budding from a human cell membrane 244

2 Procedure 1. With your partner, spread out the Cell Structures and Organelles cards on the table. Sort out the cell structures and organelles that you think the HIV virus would directly need in order to reproduce many copies of itself. Set the other Cell Structures and Organelles cards aside. 2. Discuss with your partner the path that you think the HIV virus would take within the cell as it takes over the cell. Lay out the cards in the order you decide on. 3. Pick a colored pencil, and on your Student Sheet 16.1, Scientific Diagram of HIV Infection, do the following: a. Trace the path of the virus infection through the various structures or organelles you decided on in Step 2. b. Next to each structure or organelle in the path, write an explanation of why you think that structure or organelle is involved. 4. Visit the Science and Global Issues page of the SEPUP website at sepuplhs.org/sgi. With your partner, follow the simulation of the life cycle of the HIV virus. 5. Watch the narrated version of the simulation. As you watch and listen, with a different colored pencil add to or change the path you traced, where appropriate, on Student Sheet 16.1, Scientific Diagram of HIV Infection. 6. For more detail, view the step-through version of the simulation and read the descriptions of each stage of the process. At each step you can click Play to watch the animation of only that stage. 7. Follow your teacher s directions for reading the case study about rotavirus. As you read, use the Read, Think, and Take Note strategy. 8. Complete the information for rotavirus on Student Sheet 2.1, Disease Information after you read the case study. HIV/AIDS INFECTION AND CELL ORGANELLES ACTIVITY

3 SCIENCE & GLOBAL ISSUES/BIOLOGY CELL BIOLOGY Analysis 1. Explain why HIV must infect a host cell. 2. Explain how the HIV virus uses specific structures to enter the cell. 3. a. List the structures and organelles inside the cell that an HIV virus needs if it is to reproduce. b. Describe how HIV uses each structure and organelle during the infection process. 4. In Activity 10, Functions of Proteins in Cells, you learned about eight classes of proteins. a. Which classes of proteins were shown in the HIV infection animation? b. What function did each of those classes of proteins perform in the virus infection cycle? 5. How did your ideas about the steps of the HIV infection inside a cell change before and after viewing the simulation? 6. If you were a researcher of HIV/AIDS, explain which part of the infection process you would be most be interested in if you were trying to find a way to: a. prevent HIV from entering cells. b. prevent HIV from reproducing. 7. HIV infects cells of the immune system, while rotavirus infects cells of the intestine. What structures do you think are responsible for the ability of each virus to only infect specific types of cells? 8. What evidence from the rotavirus case study explains why more than 85% of rotavirus deaths occur in Southeast Asia and Africa? KEY VOCABULARY DNA enzyme organelle protein rotavirus 246

4 HIV/AIDS INFECTION AND CELL ORGANELLES ACTIVITY 16 CASE STUDY Rotavirus GLOBALLY, ONLY A few infectious diseases cause the majority of deaths for children younger than five years old. Rotavirus, with the severe diarrhea it causes, is one of them. Rotavirus causes approximately 40% of all cases of severe diarrhea in infants worldwide. More than 85% of rotavirus deaths occur in Asia and Africa. SYMPTOMS AND DISEASE MECHANISM The symptoms of rotavirus infection include severe Burden of Disease vomiting, fever, abdominal pain, and watery diarrhea over several days. These symptoms are usually milder in adults, who normally recover. Rotavirus is an RNA virus that infects cells that line the small intestine, the ones that absorb nutrients and water. TOTAL NUMBER WITH DISORDER NUMBER OF DEATHS PER YEAR Worldwide more than 100 million 450,000 United States 55,000 70,000 hospitalizations When the virus infects and kills these cells, unabsorbed nutrients and water leave the body rapidly in diarrhea and vomit, making the patient weak and dehydrated. Rotavirus is transmitted (Continued on next page) Rotavirus deaths of children younger than 5, before widespread introduction of vaccine 247

5 SCIENCE & GLOBAL ISSUES/BIOLOGY CELL BIOLOGY (Continued from previous page) in contaminated water or food, airborne droplets, and contact with contaminated surfaces. Therefore, safe water, sanitation, and refrigeration of food are important for controlling rotavirus transmission. Model of a rotavirus ROTAVIRUS PREVENTION AND TREATMENT Exclusive breastfeeding is a strategy for preventing diarrheal infections, including rotavirus, in infants up to six months old. Exclusive breastfeeding means the baby ingests no food or drink besides its mother s breast milk. The baby is allowed vitamins, minerals, or medicines, but no water. Breast milk contains nutrients, antibodies, and other elements that boost the immune system, and breastfeeding eliminates the need for infants to eat food or take in drink that may be contaminated. In 2007, a vaccine became available to prevent rotavirus infection, and widespread distribution of the vaccine could be a major boost for prevention of the disease. The World Health Organi zation now recommends rota virus vaccine be administered to infants as soon as possible after six weeks of age. The maps on the following page show the first countries to introduce the vaccine and the approximately 80 countries that had introduced the vaccine by the end of Studies of the impact of the vaccine show significant reductions in hospitalizations and deaths. Currently, there is no drug treatment for rotavirus infection. Only oral or intravenous rehydra tion with electrolytes is prescribed. This maintains homeostasis of water and salts in the blood. CHALLENGES TO PREVENTION AND TREATMENT For HIV-positive mothers, breastfeeding is not a good option for preventing rotavirus in their infants because breast milk can transmit HIV. In these cases it is safer to feed babies a breast milk replacement, such as infant formula. But with formula, the baby does not get the antibodies to protect against diseases that breast milk would carry from mother to child. Currently there are two major roadblocks to global use of a rotavirus vaccine. First, more vaccine is going to countries where rotavirus is much less of Distribution of Improved Sanitation (% of population) 1 AFRICA THE AMERICAS EASTERN MEDITERRANEAN EUROPE SOUTHEAST ASIA WESTERN PACIFIC Data from WHO organization of world regions. 248

6 HIV/AIDS INFECTION AND CELL ORGANELLES ACTIVITY 16 a problem than to those with the greatest need for the vaccine. This is partly a matter of the relatively high cost of the vaccine, which is about $20 or more per child. Second, the rotavirus vaccines, like many vaccines, must be kept refrigerated to prevent their spoiling a difficult task in remote tropical and subtropical areas of the world that do not have a reliable supply of electricity. " In routine immunization schedule in 2007 (11 countries) Immunization support approved (3 countries) Distribution of rotavirus vaccine in 2007 National immunization programs (76 countries) Regional immunization programs (3 countries) Distribution of rotavirus vaccine in