BioEd Online

Teacher Background

The activity is comprised of two parts. The first is an essay which tells of how HIV/AIDS was first recognized among physicians. The second is an activity that helps students visualize the Human Immunodeficiency Virus (HIV) by having them construct 3D HIV particle models from paper. The model to be used represents a complete viral particle. It is a 20-sided polyhedron, called anicosahedron, which approximates the shape of the virus. The completed, three-piece model is about 500,000 times larger than an actual HIV virus particle. Students will combine their finished models into one mass in a first step toward estimating how many HIV particles could be contained inside a white blood cell before being released into the blood stream to attack new cells.

Depending upon students' grade and maturity levels, the essay, "Portrait of a Killer," may be used as teacher background information or as a student reading assignment. It is especially effective when read aloud. 

Content Advisory 

See the following resources for additional information about HIV/AIDS and advice for discussing HIV/AIDS with students.

• National Institute of Allergy and Infectious Diseases, National Institutes of Health (NIH), offers resources on understanding HIV/AIDS: niaid.nih.gov/topics/hivaids/ and aidsinfo.nih.gov.

• National Institute on Drug Abuse, NIH, offers facts about drug abuse and the link between it and HIV/AIDS: hiv.drugabuse.gov.

• The Centers for Disease Control and Prevention provides up-to-date information on HIV/AIDS prevention: cdc.gov/hiv/topics.

Objectives and Standards

Life Science

• Living systems at all levels of organization demonstrate the complementary nature of structure and function.

• Disease is a breakdown in structures or functions of an organism. Some diseases are the result of damage by infection by other organisms.

• Every organism requires a set of instructions for specifying its traits. Heredity is the passage of these instructions from one generation to the next.

• The instructions for specifying the characteristics of the organism are carried in DNA [usually], a large polymer formed from subunits.

• Cells store and use information to guide their functions. 

Materials and Setup

Materials per Student

• Cellophane tape (one roll can be shared by two or three students)

• Metric ruler with straight edge

• Pair of scissors

• Colored markers or pencils for coloring the models (not crayons)

• Fine point ballpoint pen with which to score cardstock before folding (felt- or gel-tipped pens are not appropriate)

• Copy of "Modeling an HIV Particle" sheet printed on white card stock paper (see Lesson pdf)

• Copy of essay (if age appropriate; see Lesson pdf)

Setup

1. Make enough copies of the HIV particle model on card stock paper for each student to make his or her own virus model. Make a few extra copies to use as “spare parts” and for demonstration.
   
   Tip: You may wish to enlarge the cutout of the virus model for demonstration purposes.

2. Have students work together in groups of 2–4 to assist each other, especially during model assembly and taping. 

Procedure and Extensions

Time: One or more 60-minute class periods

1. Depending upon students' grade and maturity levels, have students read the essay, "Portrait of a Killer." Then ask students, Have you ever seen a virus? [It is not possible to observe viruses directly, because they are extremely small.] Encourage students to share what they already know about viruses. List their ideas on the board. Make sure that the following facts are included.

   • Viruses are small infectious agents that require living cells to make copies of themselves (replicate).

   • Viruses replicate by invading living cells.

   • Most viruses are too small to see with a microscope.

   • Viruses are responsible for many different diseases, including the common cold, flu, small pox, and HIV/AIDS.

   • All viruses consist of genetic material (DNA or RNA) surrounded by a protective coat.

2. Tell students that they will learn about the Human Immunodeficiency Virus (HIV) by constructing a paper model that enables them to visualize a single HIV particle. The model will show both the exterior and interior of the particle and serve as a starting point to learn about the virus’s function.

3. Demonstrate how to cut and fold the model. Stress that the more carefully students cut out their models and score the folds, the better the models will look. Students should cut along the solid lines and use the ruler straight edge and ballpoint pen to score the dashed fold lines. Pressing the pen tip into the paper produces a crease that makes accurate folding easy.

4. Have students color their models prior to assembly. While virus particles do not have color, researchers often create colored models to emphasize certain structures. [See the presentation “Viruses (NCMI)” on BioEd Online, www.bioedonline.org, for examples of virus models.]

5. Demonstrate how the virus envelope is formed. Start by creasing along the edges of each triangle, and then reopening the creases. Begin taping with two adjacent triangles. Bring their adjoining straight edges together and hold with a small piece of tape. Continue taping triangles until the model gradually forms a spherical shape. Repeat until all triangles but one are taped together. The remaining triangle serves as a “door” to the inside of the virus.

6. Have students follow the same cutting, folding, and taping procedures for the HIV capsid. They also should press the capsid insert into the capsid. If the insert is loose, a small dab of glue or a small reversed tape ring will hold it in place. Temporarily slip the capsid inside the model.

7. Discuss the model’s appearance and structures as a class. Explain that the model is approximately 500,000 times bigger than an actual HIV particle. Ask, How big do you think the actual HIV particle is? [about 120 nanometers] List a few comparisons, measured in nanometers, for visualization. A nanometer is one one-billionth of a meter (approximately 0.04 billionths of an inch). Ask, How tall are you in nanometers? [Your height in meters times one billion.] 

8. Have each student measure the diameter of his/her virus model. Ask, Since the model is not a sphere, what is the best way to measure it? Discuss different ways to measure the model’s diameter (point to point, point to side, edge to edge, side to side).

9. Tell students that the white blood cell invaded by the HIV particle is 120 times larger than the particle. Ask, Compared to the HIV model, how big is a white blood cell?

10. Have all students place their HIV models into a pile to see how large the mass of models becomes. Count the number of particles in the pile. Then ask, How many HIV particles do you think it would take to fill a white blood cell? How could you find out? (It would take about 1.7 million HIV particles to fill one white blood cell completely. This calculation is based on a comparison of the volume of an HIV particle with that of a white blood cell. To compute these values with students, use the equation, volume=4/3πradius³.

11. Have students collect their HIV virus particle models and save them for use in the “Making Copies of an HIV Particle” activity.

Handouts and Downloads