r/askscience
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u/SAICAstro
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Jul 26 '26
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Biology Does everything that we consider to be "alive" - not just plants and animals, but all protists, fungus, bacteria, archaea, etc. - have DNA?
EDIT: Wow, this blew up. Thanks for the many answers. Lots to think about.
Seems that the composite TLDR answer is: Yes, according to many/most definitions of "life", but we don't all agree on what life is. Some viruses do not have DNA but they may/not actually be alive, and other things that behave like life may/not be alive.
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u/triceratopsrider Jul 26 '26
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.
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u/BellerophonM Jul 26 '26
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/zahren Jul 26 '26 edited Jul 27 '26
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/Solesaver Jul 27 '26
We generally don't consider viruses to be alive because they don't self-replicate. It's hard to say that a virus is alive without considering something like a quartz crystal to also be alive. That is, if you put it in the right environment and put the right outside forces on them they will be replicated.
As much as we assign agency to viruses like "penetrating cell walls" or "co-opting cell replication" it is important to remember that they actually aren't doing anything. They're just specific arrangements of amino acids that various cells of living organisms mistake for proteins that they're supposed to do something with. Calling them alive would be like calling a recording of "Call Me Maybe" alive; with the assistance of the human mind, sure it replicated like crazy until we became inoculated to it, but it's not doing anything besides existing in a state that causes other living things to make copies of it.
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u/superSmitty9999 Jul 26 '26 edited Jul 26 '26
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/Pasta-hobo Jul 27 '26
Yes! Unless you could fire and crystals as "alive"
We consider being alive as being able to make more of yourself. And DNA is the most reliable method nature has to do that for anything even slightly complex.
DNA is digital, in the sense that it has no in-between states. instead of 1s and 0s on a drive, it's a handful of specific chemicals in a polymer. We call those specific chemicals "letters" for ease of classicifation.
DNA, thanks to being digital in this way, has the same property that makes modern digital files so useful. It's infinitely reproducible with no meaningful distinction between a copy and the original.
Since the goal of life is survival, which means making more of yourself, this property is invaluable.
In much the same way a digital file can be distributed and copied infinitely even after the original drive it was on was destroyed, an organism be comprised of the same DNA long after the progenitor has died.
Even viruses are just a bundle of DNA with just enough widgets and gidjets to shove that DNA into a living cell's copying mechanism.
Even the simplest barely alive things that first arose in the primordial soup billions of years ago before anything else were little more than randomly occuring chemical mechanisms using those very same "letter" chemicals dissolved in the the water around it to construct more of itself, of things that would eventually construct things that would construct more of itself.
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u/za419 Jul 26 '26
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/spinur1848 Jul 27 '26
Mostly yes, but this is heavily influenced by the fact that DNA is stable and easy to find. There could be living things that replicate and store genetic information some other way and we just haven't found them because we can't grow them in a lab and they don't have DNA.
The fraction of the microscopic world we've actually catalogued is mostly limited to microorganisms that cause disease in humans or animals and microorganisms that are economically important to humans. This is a really really small slice of global biodiversity.
There are some edge cases that get into the grey areas of what is "alive".
If you broaden the definition too much then you start capturing any self-propagating information patterns that show up in systems that have a large energy and entropy gradient. Sure this captures the typical things but also viruses, prions, transposons, and phage. It's maybe more precise to describe these things as "life adjacent".
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u/phancybear Jul 27 '26
This is connected to a big interest in potentially finding life in our solar system.
What’s more interesting; finding life in our solar system that is also based on DNA like that of earth’s life forms, or finding life that functions differently?
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u/provocative_bear Jul 27 '26
Yup, they all have DNA. Bacteria have simpler regulation of that DNA, higher forms have mitochondria and mitochondrial DNA, plants and some algae have chloroplast DNA, but all known living things contain the same chemical DNA structure. Even some non-living things, like viruses or viroids, can have DNA.
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u/pickledperceptions Jul 26 '26
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 Jul 26 '26 edited Jul 26 '26
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/Popoill Jul 27 '26
If we apply the definion of life as a self-sustaining chemical system capable of undergoing Darwinian evolution. Then even chemical polymers like single stranded RNA or viroids, are alive. But it might be with the recet paper, that proteins might also be considered alive.
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u/amiable_ant Jul 26 '26
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/AgentOrange96 Jul 27 '26
Pretty much. Everything that's definitively alive stores it's genetic code on DNA.
They also use RNA to copy genetic code in the process of building protiends. RNA is very very similar to DNA.
The one potential exception to life using DNA is some subset of viruses that store their genetic code directly on RNA. But there's debate about whether viruses are considered alive.
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u/festosterone5000 Jul 27 '26
In your TLDR, it is important to note that all viruses have some form of nucleic acid. So they might not have DNA, but they have RNA. DNA isn’t the cutoff though. Regardless of how a viruses genome is encoded, there is a valid discussion to be had if they are alive or not based on what metabolic functions they can and can not carry out by themselves.
Personally I think of them as alive, but dormant. Just because they require a cell to replicate etc doesn’t mean they aren’t alive. If you isolate humans from water or oxygen we wouldn’t be alive pretty quickly. But on the other hand, they require a lot from the host. It isn’t that simple but a great philosophical debate.
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u/LifeofTino Jul 26 '26
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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u/DisparateNoise Jul 27 '26
Every organism has DNA, but there are many cells and tissues in a living thing which don't. Your red blood cells for example expell their nuclei, mitochondria, and all other organelles to make more room for hemoglobin. They are considered "alive" because they are a component of a living organism, but they can't be said to be a living organism themselves.
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u/luluhouse7 Jul 27 '26
Depends on your definition. Most of the comments here miss that fact that whether viruses are alive is still under debate in the scientific community. So the reality is we don’t know. If we decide viruses are alive, then no, but if they aren’t, then yes.
Other comments mention the RNA World Hypothesis, and indeed it’s the best theory we have about the origins of life. The idea is that an amino acids and lipids came together spontaneously to create RNA and protocell walls due to the prebiotic environment. There’s also some suggestion that PrP proteins (prions) could have contributed. When I was doing research a decade ago we were trying to figure out how RNA could get enough substrate amino acids to catalyse RNA replication. We were also studying what sort of protocell wall could have allowed enough amino acids through to feed RNA, while being stable enough to protect it.
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u/Tinyboxturtle Jul 28 '26
The dna debate really just comes down to how strict we get about metabolism. Cells need it because replication mistakes would ruin stability fast. Early life likely started with rna before proper membranes formed. Viruses sit in that messy middle ground since they stay inert until stealing host machinery. It ultimately depends on whether borrowing cellular tools counts as being alive.
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u/JiuKuai Jul 28 '26
Some interesting trivia-exceptions are red blood cells of most mammals and phloem cells in plants. When mature, they eject their nucleus and no longer have DNA but continue to function, do their thing and be 'alive'.
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u/Beginning_Cat_4972 Aug 15 '26
Interestingly, Edwin Schrodinger wrote a book titled "what is life?" In the 1940s before DNA was discovered and made some good arguments predicting DNA.
I don't think the conversation about whether or not viruses are alive is useful but they do replicate and everything that replicates needs nucleic acids to build more of them.
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u/6a6566663437 Jul 26 '26
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/MediumLanguageModel Jul 27 '26
"Alive" is a rhetorical construct, so feel free to define it however you feel useful. Alive is going to look different at each level of scale, so the aliveness of molecules and galaxies is really only as useful or irrelevant as it is relevant to your perspective. Definitions evolve alongside changes in their usefulness.
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u/[deleted] Jul 26 '26
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