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## HIV/AIDS

Author(s): Gregory L. Vogt, EdD, and Nancy P. Moreno, PhD.
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#### Making the Model (cont.)

Procedure (cont.)

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.]

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.

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 completed viral envelope.

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 (see “Note,” below). 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.]

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).

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?

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=4/3π radius3.

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

### Science Education Partnership Award, NIH

MicroMatters
Grant Number: 5R25RR018605