Viruses
A Close-Up of SARS-CoV-2
By Deborah Landry, Ph.D.
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VirusesLoading...
A Close-Up of SARS-CoV-2Loading...
By Deborah Landry, Ph.D.Loading...
© Deborah Landry, 2021-23. All rights reserved.
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Deborah Landry, Ph.D. is founder and executive director of IXplore STEM, a nonprofit formed to build science, technology, engineering and math (STEM) literacy and proficiency and to encourage K-12 students to pursue STEM degrees and careers. Dr. Landry has over 25 years of experience as a science educator and curriculum developer for K-16 classrooms. She received her Ph.D. in Molecular and Cellular Biology from Brandeis University, focusing on genes in the immune system; and is an adjunct professor at the University of New England. In her spare time, Deborah enjoys exploring the woods and waters of Maine.What is a virus?
Viruses are not living cells as they lack most of the "characteristics of life". Although viruses have genetic material –DNA or RNA– they cannot reproduce or synthesize proteins on their own and they cannot maintain homeostasis, metabolize energy or respond to stimuli. Instead, viruses infect cells, take over the cell's molecular machinery, and steal the molecular building blocks they need to build proteins and replicate.
Viruses are invisible to the naked eye, but can be seen with an electron microscope (figure 1).
Viruses are invisible to the naked eye, but can be seen with an electron microscope (figure 1).
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Figure 1: Covid-19 virus (pink) exploding from an infected cell (green). Virus particles are about 500X smaller than a human skin cell (scanning electron microscope image, Image credit (and book cover):NIAID-RML/de Wit/Fischer.
Figure 2: Viral structures for HIV (human immunodeficiency virus), bacteriophage (a bacterial virus), influenza virus (causes the flu), and SARS-CoV-2 (causes Covid-19).
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Although there are more than a million different types of viruses, they all have several structures in common (figure 2). All viral particles have genetic material—double-stranded or single stranded DNA or RNA— and a "nucleocapsid" protein cover to protect the genetic material. Most, but not all animal viruses, have a lipid membrane envelope covering as well.
Figure 3: A SARS CoV-2 virus particle showing structures and functions, including the membrane envelope and (+) single-stranded helical RNA covered by N-protein.
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A Close-Up of SARS-CoV-2
The SARS-CoV-2 virus causes a flu-like disease called Covid-19. Its genetic material is single-stranded RNA (+sense), has ~14 genes and codes for ~29 potential proteins. It has a lipid membrane envelope, which anchors several membrane proteins like the spike protein (shown in blue in figure 3). As a comparison, the human genome has 3 billion base pairs and ~28,000 genes.
Figure 4: Diagram of the SARS-CoV2 genome stretched out from beginning (5') to the end (3'). The location of its 14 genes is shown. Some genes are color coded and correspond with proteins in figure 3. A mutation in gene number 8 (*) allowed the virus to jump from infecting bats to infecting humans.
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The SARS-CoV-2 virus genome is about 30,000 bases long (figure 4). Scientists have sequenced the virus's genome and deciphered its genetic code.
The largest gene codes for a protein called RNA replicase, which is an enzyme that is needed to make new copies of the virus RNA genome.
The largest gene codes for a protein called RNA replicase, which is an enzyme that is needed to make new copies of the virus RNA genome.
Click the UC Santa Cruz genetic database link (right), then click the box marked "base" to see the RNA code (A-U-G-C) of the virus. Bioinformatic tools embedded in the website determined the amino acid sequence of the virus proteins.
Figure 6: Diagram showing the life cycle of the SARS-CoV-2 virus.