Eli5-If a virus isn’t technically alive, I would assume it doesn’t have instinct. Where does it get its instructions/drive to know to infect host cells and multiply?
In: 7067
A virus is in simple terms a container and a set of instructions.
The container typically has a few contact points that can detect when it comes into contact with a suitable host cell. At which point it attaches and dumps the instructions into the cell.
The instructions are how to take over a cell’s inner machinery and instead of doing what it usually does, only make more virus instructions and containers. The infected cell usually does this until it dies, at which point the newly made viruses are released.
The virus has little ability to sense or react to its environment, so usually just goes along inert until it comes into contact with a suitable host cell. Some viruses can’t survive long outside a host cell, some are very hardy and are able to be inert for long periods of time outside a host cell.
Whether it’s technically alive is a matter of definition.
What matters is that if you can arrange for a copy of yourself to be made, there will be more of you. Doesn’t really matter how you do it, or why it happens. Cows are alive, and contain the “machinery” for their own reproduction, but they only exist because we make copies of them. They don’t have an instinct to be farm animals, yet they have something about them that makes another life form want to make more of them. Similarly, a virus contains instructions for making copies of itself. It doesn’t need to want anything, it just needs to be a little machine that makes more little machines.
If more copies of you are made, you’re more “successful”, and those copies can start making even more copies. If you become bad at making copies, for example because a predator eats you faster than you make copies, or copies of something else takes the resources you need, then you’re less successful.
The magic happens when you make *imperfect* copies of yourself. Then they compete against each other, and the more successful ones end up making copies of themselves instead of copies of you. This selects for the best copiers because there are the most copies of them, regardless of what’s making the copies.
How does vinegar know how to fizz when you add baking soda?
It doesn’t “know” in any real sense. It’s just chemistry. Molecules bump together and it takes less energy to stick together or change shape than it would to stay separate.
Picture two drops of water on a sheet of glass. They get close, then all of a sudden they join. They look so happy together! They look as if they “wanted” to join. But it’s just molecules behaving as molecules do.
Our cells have the ability to grab molecules and bring them inside themselves. It’s used for all kinds of signaling in our bodies, for example adrenaline.
Viruses are coated with molecules that our cells think are one of these signal molecules, so if a virus particle touches one of our cells it will grab the virus at which point the DNA in the virus gets released into the cell, and the cell then unwittingly uses that new DNA to make more viruses.
Basically the virus just floats around and it’s our own cells that do all the work.
The thing about a virus is that ***all it is***… is *a set of instructions*. Crucially: it’s not alive because it doesn’t contain the instructions needed, to replicate itself.
Let’s step back, though: imagine a town full of book factories. *Millions* of factories. These factories take wood, but for everything else that’s needed to make the book, the factory does the work: it turns the wood into paper, it turns some of the wood into ink, it prints the words onto the pages, binds the pages up, makes some cardboard for the books to be shipped in, and then ships the books out at as packages to wherever the orders come from.
Let’s say one day, the head of a factory receives a package with a book in it. And the book says: “Surprise! You have been cursed by the ghost of Christmas future! Follow the instructions below to send a copy of this package to 10 other factories in this town, or you will suffer a horrible fate!”
The factory head, maybe because he is not too bright, or maybe because he thinks the joke is hilarious, builds ten copies of the package and sends them to the ten factories on his street. Soon everybody in town is sending each other joke packages!
Here’s the crucial thing: is the package alive? Absolutely not!
* The package didn’t build itself.
* The package didn’t mail itself.
* The package didn’t decide whether it gets built.
* The package doesn’t contain the instructions needed to build a package factory.
* The package doesn’t contain the instructions needed to grow or harvest any wood.
* The package doesn’t even contain the instructions needed to make its own paper.
That’s what viruses are like. I absolutely love the fact that we call chain letters and chain emails and shit “viral”, because they’re a great demonstration of just why viruses aren’t alive: they’re not alive *because* they can’t do anything for themselves.
Living cells are the ones that bring the viruses inside, just like how it takes a deliveryman to deliver a package. Living cells are the only places where the “instructions” contained in a virus can be followed; the DNA inside of a virus doesn’t do anything if it’s just outside in the rest of the world.
Viruses are not a self-contained nucleus of reproductive activity. They’re only a set of instructions that hijacks other reproductive machinery. That machinery, in order to replicate itself, has to have its own self-contained feedback loop of reproductive activity. That’s what makes viruses not alive.
Saying it doesn’t really have instinct is correct enough. A virus doesn’t need to do all that much- it happens to wander into a cell, which it’s the perfect shape for slipping into, which triggers a chemical reaction to release its genes into it.
It’s the same for why it might resist antibodies or avoid detection. It has its own DNA/RNA telling how to make it, but it doesn’t actively do much once it’s made- it relies on the infected cell carrying out its genes to do that.
You know 3D printers right? They take a 3D computer file, called an STL (we’ll call it a blueprint), and based on the instructions in that code, create a plastic object of any shape.
Your cells contain DNA, and the job of DNA is to be a blueprint. Then, ribosomes are the 3D printers which can build proteins to do anything.
Imagine you took a 3D printer, and you uploaded a blueprint for… A blueprint maker. You can see the problem – the blueprint maker would make more blueprints for more blueprint makers. Your cells end up making so many blueprints, and blueprint makers, that they overload. The cell literally gets full of blueprints until it physically pops.
That’s what a virus is. It’s a special strand of DNA that just so happens that when your cell reads that DNA, it ends up making more of itself. It doesn’t think, it doesn’t have goals, or instincts, it’s literally just a strand of DNA where the proteins it makes lead to more DNA of the same type being made.
Since RNA has existed, predating even single cellular organisms, there have been a flurry of all different kinds of RNA contained within many different ‘shells’. The RNA probably started as random and was driven purely by thermodynamic processes. I’m talking primordial viruses. They would, in some cases by chance, have the correct sequence of RNA that could hijack the cell’s system of copying and this quickly catapulted these random bits of RNA into what is now an ever-evolving cycle between these RNA bits that have been with us since the dawn of time and our immune systems fighting them off. Once it reaches the ability to hijack our cells instruction code – all that really has to happen is the cell thinks the RNA is its own DNA and begins spending resources copying that instead of important and crucial proteins and such. With the death of the cell these copies drift out into the world like landmines for the next cell to come across and be infected. Viruses are as old as life. Perhaps older.
Think of a water wheel. A water wheel doesn’t *know* it’s turning. It isn’t alive, but it turns. Attach a few gears and such and you have an automatic grain mill. Does it know it’s a grain mill? No, but it will mill grain.
Think of a block of code. A function. If you randomly assembled 1s and 0s, eventually you’d have a block code that works and does something. A virus is basically the 3D version of that, random parts coming together until it does something
The best analogy I’ve heard is that it’s like a USB drive. Doesn’t really know what it’s doing but if you plug it in, the files just do their thing.
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