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Challenge 2: How does a virus enter a host?

Learning Targets:

  • I can explain how the SARS-CoV-2 virus enters a host cell and how specificity plays a role in host cell recognition.
Estimated Time: 30 minutes


Read & Describe:

SARS-CoV-2 Tracker - Follow a single viral particle

Imagine you have a teeny tiny camera like a GoPro attached to the surface of a single SARS-CoV-2 particle, the coronavirus that causes COVID-19. This particle, also called virion, is on the smaller side of SARS-CoV-2 particles and is only 70 nanometers in diameter (a nanometer is a million times smaller than a millimeter!).

  • In the periphery of the viewing window captured by the camera, it is possible to see the surface of the viral particle. Describe what is on the surface?

The story continues...

The virion is currently in the air within the lungs of a classmate of our friends Tash, Ray, and June. This teen doesn’t know he is infected yet as up until this point he’s been asymptomatic, so he’s not wearing a mask while he rides the school bus at the end of a long school day. He’s starting to feel a tickle in his lungs and has the sudden urge to sneeze. Our virion is now in a droplet that is about 5 microns in diameter (a micron is 1000 times smaller than a millimeter!) that contains 100 more particles that look almost identical to the one we are following but vary in size.

“Aaaaa aaaaa aaaaa choo!” The student sneezes. At a speed of 100 miles per hour, the droplet is expelled from the lungs, travels up the trachea and through the mouth and enters the air of the bus where Tash is sitting several rows away.

Within minutes, Tash inhales and SWOOSH the droplet enters Tash’s nose and is whisked down the trachea and into his lungs. Once there, the droplet breaks open and the virion is released into the lung cavity. After floating for a matter of minutes, it bumps into a cell on the epithelium of the lung.

  • There are epithelial cells in the lungs as mentioned above, but also in other organs like the skin, digestive tract, etc. If “epi” is Greek for “on” or “upon,” where specifically in an organ do you think you would find epithelial cells?

After the initial bump, the virus particle bounces around a bit, but at once, seems to lock into place.

  • Draw a picture of what is happening upon host cell recognition. Provide the names of the proteins that interact on the virus and on the host cell.

The process of how the virus physically enters the cells is not completely clear. Structural biologists and virologists are working to elucidate the exact mechanism, but for now they know that the process involves the viral envelope fusing with the membrane of the host cell (fusion is the process by which two membranes join to form one contiguous membrane). This allows the virus to “infect” the host cell.

  • When the virus “infects” the host cell, what viral contents are required to enter the host cell?

Discuss & Reflect:

  1. Can the SARS-CoV-2 virus enter any cell of the body? Explain why or why not.
  2. The common symptoms of COVID-19 are the following: coughing, sneezing, congestion, loss of taste and smell, shortness of breath, vomiting, and diarrhea. Given this list, what types of cells can SARS-CoV-2 infect?
  3. Some patients with COVID-19 also have complications involving damage of organs such as the heart, kidneys, and even the brain. What does this mean about the cells in these organs? HINT: Think surface of the cell.


Data indicate that children and young adults are more likely to have asymptomatic or mild cases of COVID-19 and some preliminary data indicates they may have to do with the number of ACE2 receptors. Write a hypothesis statement about the relationship between age and ACE2 receptors. How would you test your hypothesis?