This is a discussion assignment from my online biology course. I like to write lecture content for delivery during grading. If I lay out too much content at the start of the module, my concerns become the sole concerns of the students. In my online classrooms, I lead with the learning outcomes. Students direct the learning by writing first. They write about the learning outcomes in open forums called discussions in an online course. I respond according to their written concerns and interests. In this discussion, students wrote about large charismatic animals and showy flowers. And thus, my commentary here expands the discussion and hopefully, it is particularly memorable because it is delivered last.
1. Choose one species to highlight. Write a complete citation for the reference(s) used.
I am going to highlight SARS-CoV-2, also known as COVID-19 or coronavirus. I used the following references in preparing my comments:
Davidson, M.W. 1995-2019. Virus Structure. Molecular Expressions. University of Florida. https://micro.magnet.fsu.edu/cells/virus.html
Microbewiki. last updated 3-21-20. Coronavirus. Kenyon College. https://microbewiki.kenyon.edu/index.php/Coronavirus
Wrapp, D. Wang, N. et al. 2-19-2020. Cryo-EM Structure of the -019-nCoV Spike in the Prefusion Conformation. Science DOI: 10.1126/science.abb-2507
Zhang, T., Wu, Q., & Zhang, Z. (2020). Probable pangolin origin of SARS-CoV-2 associated with the COVID-19 outbreak. Current Biology. doi: 10.1016/j.cub.2020.03.022
2. Include at least one image of the species highlighted.
coronavirus, photo credit: Microbewiki. 2020.
3. Describe the classification of the species, indicating its identity at every level of classification.
Since viruses are not alive, they do not follow the binomial classification schema created by Linnaeus in the 1700s that we still use today. Instead, viruses are organized according to the organisms they infect which includes all kingdoms of life, bacteria, plants, animals, protists, and fungi. After classification by host kingdom, viruses are arranged based on 1) the shape and size of the capsid and nucleic acid, 2) the presence of a lipid envelope around the nucleocapsid, and 3) whether they have RNA or DNA. Viruses have two primary phenotypes. They can be rod-like or an icosahedron shape, which is referred to as a spherical shape even though the molecular shape is angular.
4. Highlight the characteristics inherent to members of any one classification level.
Coronaviruses are named for their phenotypic commonalities. They are one of four families in the Order Nidovirales. All coronaviruses have a spherical shape with spikes protruding like a crown, or like the rays of the sun. Coronaviruses are positive-sense, single-stranded RNA viruses with a lipid membrane. Positive sense viruses are like mRNA and therefore can be translated immediately into proteins in the host cell. There are four structural proteins coded for in coronaviruses: the nuceocapsid proteins, the envelope, membrane and spike. Coronaviruses are rather large for viruses, approximately 125 nm. Here’s a look at the SARS-CoV-2 spike protein molecule.
coronavirus spike protein, photo credit: Wrapp, et al., 2020
Despite this dizzying complexity of this protein, we must appreciate that viruses are among the smallest functional collections of atoms on the planet. Check out this size scale: https://learn.genetics.utah.edu/content/cells/scale/. Scan to 125 nanometers. What other things are this small? Almost nothing. As an aside, this is why is it exceedingly difficult to filter viruses from water. A thread is approximately 300,000 nanometers wide. A grain of salt is 500,000 nanometers wide. Viruses are an order of magnitude smaller than any single-celled organism.
5. Describe the ecological context for the species highlighted.
Coronaviruses are predators that have animal hosts. Scientists suggest that COVID-19 was transferred from pangolins (Zhang, Wu, and Zhang. 2020). Pangolins are a wild species illegally traded for use in traditional Chinese medicine. To write plainly, this pandemic arose from a wild bush meat trade that is illegal. That should give you food for thought (sorry, bad pun). In many places around the globe, wild animals are consumed as a primary meat source. But don’t worry, domesticated animals can carry viruses too. The domestication is not what matters. It’s the fact that the hosts are animals. And probably there is something in there about the cleanliness of open air meat markets…
Pangolins, photo credit: https://www.worldwildlife.org/species/pangolin
Viruses infect the cells of their hosts through respiratory vapor transmission. In other words, coronaviruses transmit through a liquid that leaves one host and enters another host. When we talk about viruses invading a cell, we are talking about a non-living entity manipulating a cell via its membrane. Coronavirus docks onto a cell like any other protein and start its work of tricking the cell into translating its mRNA-like message. In summary, the ecological context for COVID-19 is a predatory relationship occurring in an animal host.