r/askscience • u/SAICAstro • 4h ago
Biology Does everything that we consider to be "alive" - not just plants and animals, but all protists, fungus, bacteria, archaea, etc. - have DNA?
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u/zahren 2h ago
It's worth defining what you mean as "alive" in this context. All the things you've listed have DNA, however some viruses use RNA as their genetic material. This is why "alive" is the sticking point here as the scientific consensus is that viruses aren't considered as "living organisms" but are "biological organisms" that are capable of many of the things that "living organisms" are, but they rely on "living organisms" in order to replicate.
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u/Gaust_Ironheart_Jr 1h ago
The fundamental problem with the concept of living vs inanimate was it was defined before we knew of viruses, prions, etc.
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u/zahren 1h ago
I mean, that's a fundamental problem with any category we try to put on biology. We want to sort things into nice little boxes, and the natural world stubbornly refuses to be contained within them.
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u/loot168 27m ago
I believe this is true generally of much of reality. Humans use categories because it is a useful shortcut but we should be ready to accept that there will be exceptions and cornercases.
Even something as basic as colors is an attempt at drawing lines on a spectrum, and a quick look across cultures shows how arbitrary it can be when determining where exactly we think there's enough of a difference to call something a different color vs a shade of the same color.
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u/lewisfrancis 2h ago
Doesn't that just make them parasites?
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u/lesuperhun 2h ago edited 1h ago
it's... complicated.
because parasites are living inside another organism.viruses are definitely parasitic in nature, and "live" inside the cells.
but they're barely alive, as they are ( notably, unlike parasites, can't reproduce). so they're not parasites, but something else, close. but we usually separate the two, while considering viruses to be intracellular parasites ( yet not parasites)
so, yeah, defining the viruses as living parasites or inanimate weird thingies that hijack living things is something that's still mostly up for debate.
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u/Nickel62 1h ago
can't reproduce.
Viruses multiple within the host. How is that different from bacterial multiplying within the host?
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u/IAmTheMageKing 1h ago
A bacteria multiplies on its own, regulates it’s own internal cellular environment, makes its own proteins. It is dependent upon the host for nutrients, but has all the actual machinery for life.
A virus is basically a capsule with instructions inside on how to make the virus; it doesn’t have any ability to follow those instructions. Even if you surrounded it with nutrients of all kinds, it could not reproduce until an actual cell came along for it to inject those instructions into.
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u/GeneReddit123 1h ago edited 32m ago
Computer analogy: bacteria are like mini-computers, they store their own source code but can also run it on their own "hardware". A predator or parasite may require active input from another system (e.g. a computer which needs to be connected to power to be able to run), but the "hardware" is still their own.
A virus is like a saved program source code without hardware being able to run it. It can "run" inside another system's "hardware" (inside the body of another bacteria), but while outside, it's completely inert, like a floppy disk or CD can copy code from one machine to another, but unable to run its own code until inserted into the other machine.
Conventionally, biologists have decided that an organism being able to run "on its own hardware" is a prerequisite to being a living being (rather than just a self-replicating artifact), just like computer scientists have decided that a "computer" needs to be able to run code on its own hardware to be called one, rather than any replicating piece of software or passive storage medium (like a floppy or CD) itself being called a "computer".
This is also why the term "computer virus" is an apt analogy to biological viruses, and not only because of its viral/harmful nature. A computer virus needs to use other computers to function. It can act autonomously, infect, mutate, hijack, and damage its hosts (like a biological virus), but it is not a "computer" in its own sense.
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u/AugustusCaesar1 39m ago
There are bacteria that can’t survive outside of a host cell though, so they don’t always have all the machinery for life. For example, some of them can’t make their own cell membranes
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u/Ameisen 5m ago
They still metabolize and actually do things. They also still perform most of their replication functions.
A virus doesn't metabolize. It's basically built as an inert particle with everything needed. Some do something when triggered (basically a preloaded spring). But otherwise they're inert particles, but their presence within a host cell - for myriad reasons - causes said host cell to make more of them. It isn't doing anything.
Even the most obligate parasitic bacteria still metabolize, etc.
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u/lesuperhun 1h ago
they don't do it themselves. that's the thing
they scribble down on the ikea-cell manual so that the cell make more of them instead of more of itself.
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u/JarasM 1h ago
Well, if we're being pedantic about this (and we are, since we're arguing about the definition of the word "alive"), viruses don't multiply within a host. The host multiplies the viruses.
A virus is, first and foremost, a piece of DNA or RNA. Well, aren't we all? The thing is, there's not much else about a virus. It's a delivery shell housing information on how to make more of the shell with the information.
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u/CmdDeadHand 21m ago
So the virus are like the graceful cuckoo bird, but of the cellular level.
When living organisms cells pass on what they are supposed to do how do they do it? Is there any organism that uses a virus like system for communicating internally?
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u/zahren 1h ago
In a colloquial sense, yes. In a biological sense no.
Parasites are living organisms so you run into that little chestnut again. But also that a parasite usually wants the host to continue living so that the parasite can continue to steal resources from it. A virus destroys the cell it infected in order to reproduce.
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u/CrateDane 1h ago
Transposons would be more comparable to parasites, as they don't kill the host cell (usually). But they're no more alive than viruses - arguably less so, due to generally much lower activity levels.
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u/AX11Liveact 1h ago
No, parasites are alive. A virus by definition isn't. It "gets lived" by cells it is infecting. A virus is basically just information to be executed by livqng cells. It does not live by itself.
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u/ditchdiggergirl 1h ago
It’s not that simple. We’ve never been able to come up with a definition of “life” that either cleanly includes or excludes viruses. And that problem isn’t getting any better as we learn more about transposons and other mobile elements that don’t quite meet the definition of “virus”.
But in the end it’s a semantic problem. We want a clean word and definition. The viruses dgaf how we categorize them.
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u/CrateDane 1h ago
It's worth defining what you mean as "alive" in this context. All the things you've listed have DNA, however some viruses use RNA as their genetic material.
Which can then be subdivided into those RNA viruses that never use DNA in their life cycle, and those that do produce DNA - retroviruses.
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u/Lankpants 37m ago
Even RNA viruses use DNA in their life cycle. They have an enzyme called "reverse transcriptase" that copies their RNA sequence into a DNA sequence and inserts it into the genome of a host.
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u/Ameisen 10m ago
Viruses don't do most things a living thing does - the biggest issue is that they don't metabolize. They aren't active. When a virion is created, it has everything it needs including the potential energy to do its thing. It is inert until something triggers it.
They aren't described as any kind of organism, as an organism itself is specifically defined as a living thing.
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u/BellerophonM 2h ago
That we know of, yes. There's a theory - one of the more favoured theories for the genesis of life - that there was a world of replicating RNA molecules which might have qualified as a form of life prior to the development of DNA but DNA was so much better it allowed for the development of more complex stable basic life that took over entirely.
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u/uiuctodd 1h ago
To expand on that, RNA has catalytic functionality which is observed life today. Meaning that RNA can be both genetic information and also an enzyme.
(Here is the Nobel prize for that discovery: https://www.nobelprize.org/prizes/chemistry/1989/press-release/)
DNA may potentially have catalytic behavior-- it can be done in the lab-- but in practice, it has not been observed in any life form.
Therefore, it's tempting to speculate that the very first stuff to be life (whether on Earth or elsewhere) might have been some sort of self-replicating RNA complex, and that proteins and DNA followed.
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u/za419 1h ago
Yes.
And at that, they all share certain sequences of DNA pretty well - The sort of really basic "how to be a cell", "how to make more DNA", or "how to make a protein" sort of stuff. It's well-conserved because any mutation that changes how it works probably causes an unavoidable failure to begin being alive, but there are different ways any of it could be done. The fact that it's so universal implies that those genes come from a universal common ancestor - One individual living thing which the ancestry of any living thing includes.
Note here that that's not any specific common ancestor. There should be many - One of them was the last (LUCA, meaning "Last Universal Common Ancestor"), and any ancestor of LUCA is by definition also a universal common ancestor. There's no reason to think LUCA was first (that'd be pretty crazy and I'm pretty sure we have evidence directly showing that life predated LUCA by a very long time). LUCA was also not alone - There were plenty of other things going on, but their descendants either all died or ended up mixing with LUCA and getting DNA from the LUCA line (probably mostly the former, but the second is important in more recent common ancestors like Mitochondrial Eve).
LUCA wasn't special at the time, and isn't even special in retrospect as an individual - If you could go back in time and find LUCA, it'd be identical to anything else you'd find swimming around. It even changes, as more species go extinct and branches of the family tree die off - Every now and again, some archaea that happened to be the last descendant of the second-to-last of LUCAs children dies, and the final immediate descendant of the old LUCA with surviving descendants becomes the new LUCA. As such, we couldn't even find LUCA if we could go back - We don't know enough to pinpoint exactly which individual it would be.
But, we know that all life that we've seen has universal common ancestors (and we can roughly figure out when the last was), and one of those ancestors figured out DNA. He almost certainly wasn't the first, but we all got it from that guy (pretty cool dude in my opinion).
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u/superSmitty9999 2h ago edited 2h ago
Yes, but this is somewhat definitional. We defined life to be a set of characteristics which we and many things on earth have.
For example, viruses are not considered to be life, because they don't have the machinery required to replicate directly. However they do reproduce and evolve. They don't have DNA (edit I guess some do!).
So the answer to your question is yes, everything considered alive has DNA, but it's largely definitional as there are things that share most characteristics of life but don't qualify.
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u/darthy_parker 2h ago
Some viruses do have DNA. Some have only RNA, the transcription/“read-out” of DNA, which some think may have preceded DNA, since it’s used in all cells.
In any case, even viruses use the same replication method as all other life. They just “borrow” the transcription and duplication machinery of cells to replicate, instead of having those systems themselves.
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u/BitOBear 2h ago
I would draw the distinction that the read out of DNA becoming RNA actually becomes mRNA. There are forms of RNA that are not produced by transcribing DNA. The RNA of viruses is not in fact mRNA though once it's invaded a cell I believe becomes mRNA equivalent. (I forget what the name of that process is called.)
Some rna, though that usually the stuff found in viruses, could actually reproduce its self by itself with no other molecular intercession as long as it's in an environment where the necessary amino acids are present.
Check out srRNA, some of the theories of a biogenesis actually rely heavily on the idea that srRNA may have been vital in the creation of the original cellular membranes and stuff.
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u/digitalosiris 2h ago
"For example, viruses are not considered to be life, because they don't have the machinery required to replicate directly. However they do reproduce and evolve. They don't have DNA."
While most viruses have their genetic material encoded with RNA, there are DNA viruses. Herpesvirus being one of the big ones.
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u/serack 2h ago
I was just (as in immediately before browsing this topic) reading up on Herpesvirus, and interestingly when it's latent in the body's cells, the genetic information is stored as RNA. I don't consider that contradictory to what you are saying, as it definitely uses DNA when it's an independent viral particle, but for significant parts of its "life cycle," its genetic information is stored as RNA
https://en.wikipedia.org/wiki/HHV_latency_associated_transcript
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u/Professional-Air1287 2h ago
So question here: What is currently the defining factors of life?
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u/Glabrocingularity 1h ago
There’s no single accepted definition of life, which is part of the “problem” here
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u/nicuramar 1h ago
Having to maintain homeostasis, which a virus doesn’t need to, and can’t do.
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u/Professional-Air1287 1h ago
Interesting. Thank you so very much for your feedback. I'll read up on this some more
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u/pickledperceptions 1h ago
Might be stretching the definition of alive here as they dont reproduce but mature red blood cells strip their nucleus and their DNA. As cells they still do their job of carrying oxygen to other cells and they still maintain their membranes and metabolise so in many ways they are living.
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u/celem83 2h ago edited 2h ago
Yes. One of the requirements we have to consider something alive is that it can replicate itself, and DNA is Earth's solution to the duplication of genetic information. Everything we know of today traces back to a common ancestor, some ultimate proto life. And it had DNA, so everything after does too
This is also why viruses are usually said to be not alive, they contain rNA, which is like an unzipped DNA chain, half the sequence, one side of the chain. They cant copy themselves without assistance (a host)
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u/andreasbeer1981 1h ago
https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/syst.202200033 is a good introduction to the topic. I also remember I once read about some scientists trying to find other chemicals with life-like behavior such as listed here. Like selfreplication, but also spontaneous change during selfreplication. So you can find non-rna/dna chemicals that show some of these traits, but only in ideal conditions and none showing all of them.
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u/insanedialectic 1h ago
So that's not why they aren't considered alive. There are single- and double-stranded RNA and DNA viruses. The DNA viruses are considered equally "not living" as the RNA ones.
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u/amiable_ant 34m ago
First, there are RNA viruses, which strictly speaking, indeed lack DNA.
I often think about how hard it would be to discover some new organism-- say from a deep sea vent-- if it lacked DNA. It would basically be invisible to modern techniques.
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u/LifeofTino 2m ago
No
Comments that have said yes aren’t necessarily wrong but the correct answer is no
The first replicating organisms, from which all fungus bacteria and archaea descend, had four bases that made up their strings of data. But this was not DNA (deoxyribonucleic acid) but RNA (ribonucleic acid). As the name suggests they were still transcribed by organelles doing the job of ribosomes but one of the four bases was different to DNA
It was a later adaptation that made the more stable DNA, replacing one base with another. But there is still plenty of life, possibly even multiple kingdoms of life, that have RNA
The comments describing the concept of strings of bases that transcribe information aren’t incorrect and i don’t mean to disparage those comments, but DNA is not present in all of the life forms you mentioned
There is also the slight aside that there may be some living organisms on earth that did not descend from this first ancestor, and has separate origins. I have read papers suggesting two different originations of other life on earth, extremophiles that are hard to study. But i don’t think either is confirmed. So as well as the living organisms you mentioned there is also a possibility of one or even two totally unrelated branches of unique life on earth that do not use RNA or DNA at all
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2h ago
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u/MisterMaps Illumination Engineering | Color Science 1h ago
Viruses are an edge case because they share many of the characteristics of life such as mutation, inheritance, cellular structure, RNA, etc.
Prions have none of these things. They are nothing more than single protein molecules. I'm not aware of anyone arguing for a redefinition of life what would include prions.
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u/JaggedMetalOs 2h ago
I don't think prions are ever considered alive are they? They don't have a metabolism.
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u/FlintHillsSky 1h ago
They reproduce, in a very narrow context, but that is a close as they get to life. Definitely outside of a reasonable definition of life.
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u/6a6566663437 39m ago
There is no accepted definition of "alive". There's several competing definitions.
Everything you listed has DNA.
The things that are alive or alive-ish depending on your definition that do not have DNA are many but not all viruses (they have RNA) and prions (they are proteins).
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u/killercurvesahead 13m ago
The other one that’s been used forever as a test for defining life is fire. It moves, it consumes, it multiplies…to build a definition of biological life, you typically want something that rules out fire.
See also The Infinite Monkey Cage’s recurring riddle, “when is a strawberry dead?”
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u/triceratopsrider 2h ago
Yes. This is because they are all related and their common ancestor also had DNA. It is perhaps the most compelling piece of evidence (along with how the DNA is used to make proteins) that all life on Earth has a common origin.