A virus hooks onto the outside of one of your cells. It pushes itself in or tricks the cell into engulfing it, and then it hijacks your cell’s machinery to turn your cell - yes, part of your body - into a virus factory. All of the cellular components that are usually fine-tuned to keep that cell alive, to allow it to divide into two daughter cells, to respond to changes such as when you eat or exercise, all of that machinery is captured and used to make copies of viruses.
More and more and more are produced until eventually the cell literally bursts apart and new viruses flood your body.
My name is Stephen Rader and I am a biochemistry professor at UNBC. I happen to study ribonucleic acid, RNA, and since we have all been reading that COVID-19 is caused by an RNA virus, I thought it might be informative to write a few columns on viruses, RNA, and the molecular biology of the pandemic.
So what do we mean when we say that SARS-CoV-2 (the virus that causes COVID-19) is an "RNA" virus?
Like all living things (and I will talk more about whether viruses are alive in a later column), viruses have to do two things: they have to get energy from their environment to allow them to assemble and procreate, and they have to transmit the instructions for making themselves to their progeny. In SARS-CoV-2, these instructions are made out of RNA.
In people, these instructions are made out of DNA, a close cousin of RNA. In fact, a piece of DNA is nearly identical to a piece of RNA, distinguished principally by the fact that it is missing an oxygen atom, which makes it less likely to fall apart over time. These instructions are your genome.
Viruses have genomes too. Many of them have genomes made out of DNA, in which case your cells can copy the viral genome very easily, the same way they copy their own DNA. After they have made new copies of their DNA genome, they have to package it with other viral proteins, such as the capsid shell that encloses many viruses. To make proteins, the DNA is first copied into RNA, and the instructions in the RNA are the blueprint your cells use to make viral proteins.
This is exactly how your cells make your own proteins. The virus is simply using the tools that are already present in your cells to make more of itself.
Coronaviruses are clever because they leave out the DNA step. Instead of having DNA genomes that get copied into RNA, their genomes are made out of RNA, and are therefore already the blueprints for making proteins. Some of the viral proteins that your infected cells produce have the job of making copies of the virus’s RNA genome.
This business of copying RNA into more RNA is something that your cells would normally never do. Scientists give the machinery the name RNA-dependent RNA polymerase, which simply means that it copies RNA from RNA instead of from DNA.
Why do we care that SARS-CoV-2 is an RNA virus instead of a DNA virus?
There are two reasons: the first has to do with detection, the second with finding a cure.
When your body is infected with a disease-causing pathogen, whether that is a virus, a bacterium, or something else, your immune system usually detects the pathogen and mounts an immune response. Physicians can tell whether you have had a particular disease by testing to see whether you have antibodies against the pathogen.
So far, we do not have an antibody test for SARS-CoV-2, but scientists are working hard to figure out how to make one.
So how do we detect the virus? We use its RNA genome. Using a technique (the polymerase chain reaction, or PCR) that amplifies one copy of the genome into gazillions of copies, we can easily detect even very small amounts of viral genome in the sample. But the reaction is different if we are detecting RNA than if we are detecting DNA - there is an extra step at the beginning to copy the RNA into DNA so the PCR reaction can work.
So we need to know that SARS-CoV-2 is an RNA virus in order to know how to detect it.
As for finding a cure, we want to mess up something the virus needs to do to reproduce itself, without killing the patients. What if we prevent your cells from making proteins from the viral blueprints? Unfortunately, your cells make those proteins in exactly the same way they make your own proteins. If you block the protein-making machinery, you would die.
This is exactly how the infamous and incredibly potent toxin ricin works.
So what do RNA viruses do that your cells don’t already do? They copy RNA into more RNA, remember? Your cells never do this on their own. So many labs are looking for drugs that would specifically block that step of the viral reproduction cycle. Hopefully, they find one soon.
Next time: more about RNA, genomes, and why our genomes are made of DNA.
- Stephen Rader is a professor of biochemistry at the University of Northern British Columbia. His laboratory studies how RNA is processed by our cells, and he is the founder of the Western Canada RNA Conference.
