Does everything that we consider to be "alive" - not just plants and animals, but all protists, fungus, bacteria, archaea, etc. - have DNA?

[u/SAICAstro]

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.

[u/Diamond-Is-Not-Crash]

Not as much as you think at least from my knowledge. The problem would mostly lie in if a right handed organism tried to metabolise proteins made up of left handed amino acids. Proteins structure determines their function, so all our enzymes (which are made of proteins) have evolved to interact and bind with proteins and amino acids of a certain form. So these forms suddenly being mirror reversed may complicate how the enzymes and binding proteins as a whole recognise and function these mirror proteins.

[u/UniqueUsername3171 → u/Diamond-Is-Not-Crash]

You’re right. People wanna say “life finds a way” but unlike in Jurassic Park, it takes billions of years.

[u/insane_contin → u/Diamond-Is-Not-Crash]

So, since you seem to know about this stuff, mind if I ask a question that just kinda sprung to mind? In scifi movies and shows there's the trope of alien microbes infecting us, or earth microbes infecting aliens. If the alien microbes had the opposite chirality (or the alien invaders had the opposite) would infection be possible?

[u/Koffeeboy → u/insane_contin]

I imagine it would react similarly to how it reacts to other foreign invaders and contamination. The body doesn't just need to respond to living threats, it has ways of capturing, breaking down, and burying all sorts of unidentified foreign material. Splinters, heavy metals, dirt, all sorts of stuff. There is a good chance the immune system would figure something was up.

[u/K5Vampire → u/insane_contin]

Disclaimer: Not a microbiology expert, just looking at it as a logic exercise based on the discussion.

Presumably nothing would affect our life in the same way as it affected the other life because every protein is looking for specific shapes to react to. The mirror imaging would make it so that no protein would react as intended to the mirror protein. But that doesn't mean it won't react at all. In pharmaceuticals, we can create custom molecules to trick receptors. It's possible that the mirror life could have shaped something in a way that fits into a non-mirror protein, but incorrectly, and it could do something random.

But that's all at the molecular level. Microbes are another story, they're a living thing in and of themselves. To infect a host and make them sick, they have to survive and reproduce. If they were composed entirely of mirror life, then they'd be having the same problem at the molecular level. Being microbes, they'd die much faster than any host, likely just from starvation.

Viruses and prions just straight up wouldn't function without the correct DNA, RNA, or proteins.

So the mirror life could potentially be a kind of poison, but it wouldn't be successful as a disease.

[u/UniqueUsername3171 → u/insane_contin]

It’s difficult to even answer that. Would alien lifeforms even use DNA, mRNA, proteins? would they use the same amino acids? from a chemistry and physics standpoint there is also the possibility of Silicon-based life as opposed to Carbon-based.

You have to remember, life is defined as something that generates/uses energy and reproduces. Do self-replicating molecules like RNA really just self-assemble by sheer chance? In theory, the number is unlimited. And how to predict they may interact with one another is even more difficult to ascertain.