COVID-19 Under a Microscope
In this series of posts, we will talk about the biological side of COVID-19, as understood by a high school student. Click here to view previous articles.
Schools and jobs across the nation have closed. We hear of the numbers rising every day. As of today, the worldwide confirmed cases toll is nearing 1.3 million. Scientists all around the world are working on developing more reliable treatments or potentially a cure. As days pass, new questions are emerging about why the virus functions the way it does. Before any questions can be answered, it is important to understand the basics.
What is COVID-19?
COVID-19 is a disease caused by a virus called SARS-CoV-2, a new type of Coronavirus. The name originates from the Latin word corona, meaning crown, as the spike protein-covered membrane creates a crown-shaped appearance under a microscope. Coronaviruses are a group of related viruses that causes infections in mammals and birds. In humans, it can cause an infection in the lungs or the gut. SARS-CoV-2 targets surface proteins called angiotensin-converting enzyme 2 (ACE2). ACE2 enzymes are present in large numbers in the alveolar cells in the lungs, explaining why the respiratory system is largely affected.
What is the virus made of?
Virus particles are called virions. The SARS-CoV-2 virion has six main parts: the lipid membrane, spike proteins, envelope proteins, nucleocapsid proteins, membrane proteins, and the RNA genome.
The outer layer of the virion is the lipid membrane, which holds the three structural proteins — spike, membrane, and envelope. The spike proteins are the most notable feature of the virion. These proteins, located on the surface of the cell, play a key role in infecting cells. Membrane proteins and envelope proteins are located between spike proteins on the cell surface. The membrane protein is the most abundant structural protein and studies show that it promotes curvature, giving the virion its shape. The envelope protein, like the membrane protein, is a transmembrane protein that assists in the production and release of new viruses. Both the membrane and envelope proteins play additional roles as well. Enclosed by the lipid membrane are nucleocapsid proteins that make up the nucleocapsid. The nucleocapsid surrounds is bound to and surrounds the RNA genome.
How does it replicate?
First, the spike protein binds to ACE2 on the cell surface. Next, a protease on the exterior of the cell called transmembrane protease serine 2 (TMPRSS2) assists the virion with entering the cell. Proteases are enzymes that can cleave other proteins. TMPRSS2 cleaves open the spike protein, exposing a fusion peptide, which allows the virion into the cell. SARS-CoV-2 then releases its RNA genome into the cytosol of the cell. The goal of a virus is to replicate in the host. However, cells have no interest in replicating RNA genomes. As a result, the virus has to create a mechanism for RNA replication. Approximately two-thirds of the SARS-CoV-2 genome consists of a replicase gene. The host cell’s ribosomes translate this segment of the RNA, producing two polyproteins that form a replication complex that serves as a mechanism for replicating the viral genome. Following the replication and synthesis of structural proteins, the cell begins to assemble new virions. The assembly process occurs in the Golgi Apparatus. Lastly, mature SARS-CoV-2 are released from the cell through exocytosis, allowing the virions to infect other cells in the body.
What does this mean?
There is yet a lot to be discovered about the structure and function of SARS-CoV-2. With new research emerging every day, the publication of information is crucial. It is frustrating to see how underprepared communities and the nation as a whole was for this crisis. Students, the leaders of the next generation, must understand how diseases as such can break out. Only then will the correct precautions be taken in the future. Next, in this series, we will explore the components of the viral genome, and how detailed examination of it could lead to a potential cure.
References
Coronavirus disease 2019. (2020, April 07). Retrieved from https://en.wikipedia.org/wiki/Coronavirus_disease_2019#Pathology
Fehr, A. R., & Perlman, S. (2015). Coronaviruses: An overview of their replication and pathogenesis. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4369385/#R13
Marshall, M. (2020, March 19). We’re beginning to understand the biology of the covid-19 virus. Retrieved from https://www.newscientist.com/article/mg24532743-500-were-beginning-to-understand-the-biology-of-the-covid-19-virus/
Matsuyama, S., Nao, N., Shirato, K., Kawase, M., Saito, S., Takayama, I., . . . Takeda, M. (2020, March 31). Enhanced isolation of SARS-CoV-2 by TMPRSS2-expressing cells. Retrieved from https://www.pnas.org/content/117/13/7001
Neuman, B. (n.d.). Virologist Explains What The Coronavirus Does to Your Body That Makes It So Deadly. Retrieved from https://www.sciencealert.com/why-is-this-coronavirus-so-much-more-dangerous-a-coronavirus-expert-explains
Understanding SARS-CoV-2 and the drugs that might lessen its power. (n.d.). Retrieved from https://www.economist.com/briefing/2020/03/12/understanding-sars-cov-2-and-the-drugs-that-might-lessen-its-power
