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
In the simplest of terms, in a same way that a rock knows how to roll downhill – rock doesnt really know anything, but the laws of phisics make the rock roll down. Biology is chemistry, and chemistry is physics.
Everyhting is just an ongoing chemical interactions between reactive elements.
In essence, a virus is a complex combination of chemicals, that just happened to react in particular way when encountering another particular complex combination of chemicals (host cell), that results in chemical interaction and duplication.
A virus doesn’t even have a nervous system or any organs for that matter, so it can’t have instincts, that’s correct. It can’t move or do anything either. A virus is not an animal, and no, it is definitely not alive. A virus is just a bunch of DNA in a tiny container. If it happens to touch a cell, the cell gets confused and thinks this is its own DNA and starts replicating it, creating many more viruses. Most of these viruses will never get anywhere, but a few will randomly get near other cells because of the movement of bodily fluids or the wind or people coughing, and so they can be replicated again.
It doesn’t have or need “instinct”. It’s like a little clockwork machine full of gears. What happens when it moves can *look* like a living thing, but it’s a completely inanimate object operating on mechanical principles. When one gear turns another gear, there’s no “instinct” required for the second gear to “know how to move”.
Same way our antibodies fight the virus, by reacting to stimuli. There are plenty examples of life reacting or achieving sometimes with knowing it or without instincts guiding it. Your blood doesn’t require knowledge or instincts to clot when you get a cut.
It is speculated that viruses long ago have been a part of cell machinery. E.g. every living cell has some systems that are responsible for making certain proteins, storing/reading genes, making copies of genes, etc.
One example of such a system is a plasmid – small circular DNA molecule that is able to travel from one bacteria to another. Their primary function is to provide cell with extra genes that may be useful for defense or for poison resistance. Also, some plasmids contain genes that specify how to make a plasmid itself.
Once plasmid has entered some foreign cell it is being read automatically and continuously by the cell machinery. And if it contains genes for self-replication, there will be new plasmids made, same as original.
Some plasmid could randomly mutate and incorporate some extra gene(s) which would help it replicate faster and degrade slower. These upgraded plasmids will soon out-compete old “inefficient” versions of themselves.
Another mutation could add some protective layer for the plasmid, which would help it to travel for longer distances between cells. Again, these extra-hardy plasmids will eventually out-compete more vulnerable ones.
After a few millions of years of such competition process you’ll get first viruses – pieces of DNA that tailored more to self-replication than to the cell survival.
There is no need for instincts – there are just all kinds of random mutations that happen all the time, and some of these mutations would help virus to infect & replicate, while others would hinder its spread. Those virus particles that got “good” mutations spread faster and infect more cells. That’s all to it.
Think of it like a computer program. Even though it can make decisions in the right environment and accomplish its goals we don’t consider it to be alive.
Imagine you had an IKEA instruction manual. It tells you to get some paper, some ink, and 2 staples and make a copy of the manual. It also tells you to stick it in a box and leave the copy on your neighbor’s porch.
Is there a purpose to doing this? No. But there are now two version of it anyway. Does it have guiding instincts? Still no, but it didn’t need them. It got in your home somehow and used you to make a second copy which is about to infect your neighbor. Similarly, viruses give instructions to your cells to make copies. There are some safeguards against this, but in general, you just churn out new versions that infect others, repeating the process.
Why we have different effects of viruses very simply boils down to (1) how they get into your house (cell), (2) how they tell you to make copies, and (3) how they stop the cops from busting your illegal IKEA instruction manual production ring.
1. Viruses are dumb, but they can recognize certain things. Covid, for instance, has patterns on it that match up to something called the ACE-2 receptor. This is a pretty common receptor, but there is a lot of it in the nose and lungs (where are most of your symptoms?). This starts a series of steps that results in the replication material getting inside.
2. Once it is inside, the virus has to get your body to make copies. Some viruses (ie: Herpes/HIV) are long term because part of their instruction manual told the previous host to make some machinery that busts open your DNA and inserts the virus. Others are more short-term and simply tell your cells to make a bunch of copies really quickly.
3. One of the most important parts of viruses is how they stop your immune system. Your cells tend to occasionally display what they are currently working on, analogous to a window into the house. Your immune system has a black-list of certain compounds and will straight up burn the house down if you aren’t working on something it approves of. Certain viruses, like influenza, are able to mutate though. While your immune system is looking for the red IKEA catalog, the flu has 1000’s of variations of the catalog. While you are immune to any red IKEA catalog versions, you have to learn that the blue I-KEA catalog is just as bad.
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This is one of the coolest things about “life”. And why maybe a virus is alive, and maybe it isn’t. A virus copies itself – that’s all it does. It doesn’t move around except by being swept around by outside forces. It doesn’t eat. It doesn’t breath or absorb nutrients. It is simply a set of instructions that, once inserted into a living cell, says “make more of this”. And that’s exactly what the cell does. Honestly it isn’t anymore alive than a computer virus and a computer virus “does” a lot more stuff than a biological virus.
But, and this is the cool thing, through random mutations and absorbing junk DNA viruses change their genetic code subtly and when those changes result in more copies of it being made then you’ve got a new version. When those changes result in fewer copies being made, then it dies out.
That evolutionary pressure makes it appear that viruses have desires and motivations, but it is simply a direct effect of the laws of physics.
in some way you can say a virus gets it’s ‘instinct’ from the cells it infects, a virus without a cell is as inanimate as a rock, but if you put said virus inside a cell it becomes as active or inactive as it’s host cell, like turning the power on for a computer, and regarding where it gets it’s instructions, because we only see viruses that managed to survive, as far as we can determine, it’s just random chance that certain random sequences of DNA/RNA can replicate and become viruses and cause the flu
A virus is a non-living piece of biological material. It cannot eat, it cannot move, it cannot do anything on its own. It has no drive, motives, instincts, or thoughts.
A virus gets it’s genetic material into a cell, and the cell uses that to make all the pieces to make new viruses, which it does until something else stops it (the cell dying, for instance).
An analogy might be if you stood next to a jet airplane with the turbine running, then picked up a piece of scrap metal and tossed it into the the engine. All sorts of pieces of metal shoot out of the jet engine as the original piece tears through it. Each one of those is capable of being tossed into another jet engine and producing lots of other bits of metal. The metal scrap does this by using up the engine’s own fuel, energy, and materials to produce to pieces of scrap; all it needed was the occasion to happen into the intake of the engine — and that’s all the new pieces need.
Exactly how the virus gets its genetic material into the cell varies, but it’s typically a matter of some part of the virus having a specific shape on it’s surface whereby it gets caught on the cell surface and tugged into the cell, which breaks it apart as it would other things that get in. The genetic material might be DNA that is drawn into the nucleus, or RNA that the cell acts on immediately. In any event, the cell blindly processes the genetic material if it were native and makes virus parts.
Cells make lots of viruses, and while the genetic machinery is really good, it’s not perfect. Mistakes are made, and the viruses change over time. If the bits that help it get into a cell change too much, the virus can’t infect and those ones never go anywhere. If, however, it makes it more effective, the virus spreads faster. The closes thing the virus has to “drive” is that natural selection is only going to let the viruses that infect well continue to infect, and the better, the wider the spread.
The organism and the environment do the movement for the virus, which might float through the air or water, or be passed around in bodily fluids. Maybe the blood will carry the viruses around a body, or lungs slosh them about and fire them through the air with a sneeze or cough.
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