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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?

MATERIALSFOR 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

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HIV/AIDS INFECTION AND CELL ORGANELLES • ACTIVITY 16

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 appro-

priate, 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 Infor-

mation” after you read the case study.

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SCIENCE & GLOBAL ISSUES/BIOLOGY • CELL BIOLOGY

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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 pro-

cess 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 protein

enzyme rotavirus

organelle

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HIV/AIDS INFECTION AND CELL ORGANELLES • ACTIVITY 16

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 diar-rhea 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

vomiting, fever, abdominal pain, and watery diarrhea over several days. These symptoms are usu-ally milder in adults, who nor-mally recover. Rotavirus is an RNA virus that infects cells that line the small intestine, the ones that absorb nutrients and water.

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 dehy-drated. Rotavirus is transmitted

(Continued on next page)

CASE STUDY

Rotavirus

Burden of DiseaseTOTAL NUMBER WITH DISORDER

NUMBER OF DEATHS PER YEAR

Worldwide more than 100 million 450,000

United States 55,000–70,000 hospitalizations

20–60

Rotavirus deaths of children younger than 5, before widespread introduction of vaccine

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248

(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 rota-virus transmission.

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 vita-mins, minerals, or medicines, but no water. Breast milk con-tains nutrients, antibodies, and other elements that boost the immune system, and breast-feeding eliminates the need for infants to eat food or take in drink that may be contaminated.

In 2007, a vaccine became avail-able to prevent rotavirus infec-tion, 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 adminis-tered to infants as soon as pos-sible after six weeks of age. The maps on the following page show the first countries to introduce the vaccine and the approxi-mately 80 countries that had introduced the vaccine by the end of 2015. Studies of the impact of the vaccine show sig-nificant reductions in hospital-izations and deaths.

Currently, there is no drug treatment for rotavirus infec-tion. 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 for-mula, 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

33 87 60 93 37 69

1. Data from WHO organization of world regions.

Model of a rotavirus

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HIV/AIDS INFECTION AND CELL ORGANELLES • ACTIVITY 16

a problem than to those with the greatest need for the vac-cine. 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 subtrop-ical 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)

National immunization programs (76 countries)Regional immunization programs (3 countries)

Distribution of rotavirus vaccine in 2015

Distribution of rotavirus vaccine in 2007