UNBC’S STEPHEN RADER
EXPLAINS THE ANATOMY OF A VIRUS, PAGE
Viruses carry different kinds of genetic material - DNA or its cousin RNA (ribonucleic acid). So how a virus work: what does it eat, what does it excrete and is it alive?
If you are in a hurry, the answers are nothing, nothing, and no.
SARS-CoV-2, the virus that causes COVID19, is made of the bare minimum of parts to make more of itself, and essentially nothing else.
That’s all it is and all it does. What’s the point?
There is no point. Any complex system that allows things to reproduce is susceptible to parasitism, whether it is a computer copying software or a human making more cells.
So what does a virus need in order to make more of itself?
Its genetic instructions, the blueprints that tell its viral offspring how to make more of themselves, have to be copied. That is accomplished by the proteins of the RNA-dependent RNA polymerase that I previously mentioned is an important target of anti-viral drugs.
So SARS-CoV-2 needs a few proteins to copy its RNA genome into more RNA genomes that it can stuff into new viruses.
The other thing it needs are the proteins for its shell or capsid.
Some of these form a spike that sticks out and hooks onto human cells. Part of the spike appears to be new, in that it is not seen in coronaviruses that infect other animals.
The new part may be what allowed SARSCoV-2 to jump from its natural host (maybe bats) to humans.
This is part of what makes viruses so successful and so dangerous to us: they copy themselves poorly, which means they are constantly changing and thereby finding new organisms to infect.
So the viral RNA has the instructions to make RNA-copying proteins and shell proteins.
And that’s about it. Instructions for about 30 proteins. When you consider that the next-simplest organisms, bacteria, have hundreds or thousands of genes you can appreciate that viruses are pretty stripped down.
If cells were automobiles, viruses would be skateboards.
And that is because they don’t have to eat.
Any other organism has to take nutrients from its environment. In other words, it has to eat.
For a yeast that may mean slurping up sugar (that’s how yeast turn barley malt into beer).
For a bacterium that may mean sucking up bits of protein that float around it. In either case, the cells use those nutrients in part to make energy that drives everything else they do.
Amazingly, many organisms get the energy out exactly the way a car does with gasoline: they burn it.
Of course, they don’t have actual flames inside their cells, but they have proteins that allow oxygen to react with fuel in reactions that are identical to combustion in cars.
So why don’t viruses need energy? Because they are hijacking the molecules and energy of the host cells they infect!
When a coronavirus enters a cell lining your lungs, that cell is already burning fuel to make its own proteins, RNA, DNA, and so on.
All the energy the virus needs is already there.
Therefore, since it doesn’t need to eat, it also doesn’t need to excrete anything.
Its host cell has to get rid of waste products, of course, just as your car vents exhaust.
But your skateboard doesn’t have to, because you are the motor for your skateboard.
That brings us to the question of whether viruses are alive.
Scientists don’t always agree on what we mean by alive, but viruses do a lot of things we associate with life, like making copies of themselves.
But because they don’t eat and don’t excrete and are therefore using their host’s energy, most virologists are comfortable saying they are not actually alive.
In fact - and this is really crazy - once a virus is copying itself in your cells, it looks exactly like the rest of the stuff in your cells.
It becomes you.
There is no boundary between you and the virus.
Some viruses, like the human immunodeficiency virus (HIV) that causes AIDS, literally insert their DNA into the host genome. That is why it is so hard to cure AIDS: the HIV genome is lurking in the patients’ DNA, waiting to be reactivated to make more viruses.
Viruses are just simple robots that take advantage of all the specialized molecules that are already present in the cells they invade, and they use those molecules to make more viruses.