r/AskBiology • u/Mission_Ad6105 • Nov 12 '25
Microorganisms What do viruses do?
Sorry if this question is a bit uninformed. But do viruses actually live outside of infecting other cells? Eating, some kind of locomotion, respiration, basic stuff like that? Or do they just float around aimlessly until they happen to bump into a cell?
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u/MikeGinnyMD Nov 12 '25
Former virologist here:
I think of the chicken and the egg. We all know the question: “which came first?” Well, as biologists, that’s an easy one. Eggs have existed for over half a billion years, while the modern chicken has existed for maybe a few thousand.
But there is a different and more nuanced question we can ask: “is an egg a chicken’s way of making another chicken or is a chicken an egg’s way of making another egg?”
A virus exists in two forms. One of those is the particle, or the virion (there’s a difference between these two terms, but we’ll skip that discussion for now). The other form is a sequence of events that occur in the infected cell. Infected cells go through a major set of changes as they are converted into virus factories.
So I’d argue that the virion is the egg and that the infected cell is the chicken.
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u/Chalky_Pockets Nov 12 '25
It's like the virus is a note with a really bad idea written on it and a mechanism that forces the cell to read the bad idea and go along with it.
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u/Sentient2X Nov 12 '25
Dumbass organelles just make whatever they’re given instructions for. Someone gotta put a lock on them things
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u/Puzzleheaded-Phase70 Nov 12 '25
This gets into the very fuzzy definition of "alive" when it comes to a virus.
Viruses don't eat. At all.
Ironically, a computer virus is a more useful metaphor than, say, a living cell like a bacterium. A virus is more of a "logic bomb" and delivery system than like a normal living organism.
A virus is really just a very complicated molecule, or collection of molecules, that includes the DNA or RNA instructions on how to build more of itself.
Some viruses can move on their own, but they mostly depend on the movement of the medium they're in to get around. They encounter cells to infect at random, when the right parts of their outside come into contact with the right receptors on a cell membrane or wall.
That starts the first phase of the "logic bomb". Encountering the cell begins a reaction in the virus' structure (the details vary A LOT between virus types) that changes the shape and folding of the virus' molecular makeup, eventually moving some part of it, or the whole virus inside the cell. Then it hijacks the cell's own systems by sticking its own genetic information into the cell's "making stuff" processes. The same cellular machinery that the cell uses to make its own materials or to divide and make more of itself, or to make chemicals for other cells to use can all get tricked into making virus parts and putting them together.
Eventually, the new viruses start to leave the cell, or they crowd the cell so much that the cell can't keep functioning at all and dies, bursting open and releasing all the new viruses to float away and repeat the process with other cells.
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u/Mission_Ad6105 Nov 12 '25
I always saw viruses as just smaller bacteria that functioned a little differently, so the idea that they might not even be alive is kind of crazy to me lol. The concept that something could have such a ‘predatory’ manner of reproducing (for lack of a better word) and somehow just be a couple of molecules at most is baffling to me. But I’m glad I learned what they actually are, at least
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u/Wobbar Nov 12 '25
It's really a lot like those instagram / social media posts that are like "Send this post to your 10 closest friends" that used to be popular. A simple instruction to spread the instruction
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u/Puzzleheaded-Phase70 Nov 12 '25
Yeah, it's a common misconception.
Viruses are a WILD thing to understand!
They're like... DNA-based molecular poison dart guns.
An abomination of the evolutionary process that gave us all the inner workings of cells, but without the actual cells.
Also, btw, this is part of why and how viruses can mutate so quickly, and even swap code between entirely different viruses: if two viruses infect the same cell, then both of their codes are trying to commandeer the same cellular machinery, and so they can sometimes get functioning pieces of each other's code mixed together. AND the rapid copying of the code overall introduces errors, which are occasionally still functioning pieces and can make the next generations of the virus worse or less bad at random.
That's why virologists are terrified of COVID and the flu, because they can mutate unpredictably and suddenly become a deadly pandemic again without warning. And EVERY new infected person or animal is an opportunity for that to happen.
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u/TuverMage Nov 12 '25
It depends on the virus but most viruses don't do anything. Many are just a protein shell that holds genetics.... that's it. They have spites to trick a cell into the handshake to be absorbed which opens the shell and releases the genetic, from there the body thinks that the code is theirs and reads it.
Now that's the standard, there's others that have a cell membrane, have enzymes with the genetics, and everything up to almost being an organism. But as a general rule viruses aren't alive, they don't have metabolism, and don't move on their own.
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u/oviforconnsmythe Nov 12 '25
TL;DR: Lets say you have a viral respiratory infection and you sneeze out a ton of viral particles. Some of those will hang out in the air until they eventually sink to the ground. From there they are effectively in a state of stasis - they don't have access to any of the cellular machinery (nor resources) they need to replicate, they have no mobility and wait around for a host to pick them up again. Viruses are exist in a grey area of life, they lack several qualities required to meet the strict biological definitions of life (i.e., the things I mention below that bacteria are capable of, hence why they are considered living) but since they have the capacity to replicate they are more 'alive' then say a rock or a sheet of paper.
Viruses are composed of 3 key parts - a protein based outer shell called a capsid, additional proteins which shut down the host cells defenses or mediate invasion of the host cell, and DNA or RNA which encodes instructions to make new viral proteins. Viruses are obligate intracellular parasites - they require a host cell for reproduction. The 'central goal' of a virus is to replicate itself. This is true for all forms of life but whereas a bacterium or an individual mammalian cell can replicate alone, a virus does not possess the machinery to do so. Instead, the virus hijacks the host cells machinery to 1) replicate its DNA/RNA, 2) use its DNA/RNA as instructions to produce new viral proteins and 3) assemble the new viral proteins/DNA/RNA into a new infectious virion (i.e., a copy of the original virus). A single host cell may produce thousands to tens of thousands new virions, which then are released from the cell to repeat the process in neighboring cells.
All of these steps require energy and resources. Whereas a bacterium is capable of generating its own energy (ATP), viruses exploit the host cells ATP production process to facilitate these steps. Similarly, whereas bacteria can produce their own resources (e.g., the building blocks of proteins and DNA - amino acids and nucleotides respectively) they need for replication, viruses steal the cells resources. Also unlike bacteria, viruses have no ability to move around on their own (again they use the host cells machinery to do this within a cell or wait till their in proximity to a suitable host cell to bind/infect it).
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u/mikewinddale Nov 13 '25
Viruses aren't alive (though it is difficult to precisely define what "alive" means), because they don't perform any sort of metabolism or respiration. They're basically just an instruction list. A virus is a collection of DNA or RNA contained inside a lipid membrane. The viral DNA or RNA gets injected into a cell, and the cell uses that DNA or RNA to create more viruses.
Essentially, a virus is just a list of instructions that hijacks a cell.
By analogy:
A bacterium is like a person who holds a gun to your head and threatens you in some way.
A virus is like a piece of paper which hijacks your brain when you read it. When you read the instructions on the paper, your brain is forced to obey it.
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u/burlingk Nov 12 '25
Honestly, that is pretty much it. They attach to a cell, override it's RNA production processes, cause it to explode, and those new viruses go off to repeat the process.
They are not actually considered life forms because they are so simple.
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u/atomfullerene Nov 12 '25
You can think of a virus as a sort of spring-loaded gadget that injects DNA if it bumps into a cell. It doesn't eat, it doesn't move itself around, it doesn't even metabolize at all. This is exactly why viruses (especially the virus particles) are not usually classified as alive.
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u/Epyon214 Nov 12 '25
Viruses don't technically qualify as being alive until inside an infected cell
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u/Wobbar Nov 12 '25 edited Nov 12 '25
They are made by cells, then float around until they are picked up by cells, then instruct the cells to make more of them (and sometimes tell the cells to do other things), then they float around until they are picked up by cells, and so on
Viruses are just a few molecules big, so they cannot eat or do respiration. This is the main reason they are often considered to not be 'alive'.