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RaptureAusculation t1_jbnh8ry wrote

Reply to comment by FrostReaver in I just learned that the known shortest DNA in an “organism” is about 1700 base pairs in a certain virus. Is there a minimum amount of “code” required for an organism (or virus) to function in any capacity? by mcbergstedt

Would this be a likely candidate for what the first life on Earth looked like since the structure is so simple?

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Jale89 t1_jbnneoi wrote

No: this is more like comparing a Raspberry Pi to a full modern PC - all the same modern bits but simpler. Comparing to the first life on earth would be like the first computers, with radically different components and operating principals to achieve the same functions.

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Ragondux t1_jbni1gv wrote

For this to work you need to have a cell will enzymes and ribosomes to be able to use the DNA to make proteins It's likely that the first living organisms were simpler and then built all this machinery.

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FrostReaver t1_jbnianq wrote

The first cells could've been a couple strands of RNA in a micelle with a protein.

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Ragondux t1_jbnieqh wrote

There's even a theory that proteins appeared later, since RNA can do a lot of stuff by itself and have enzymatic functions.

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Beliriel t1_jbnsf2e wrote

Yeah the base pairs of RNA can spontaneously form in nature and RNA can act like an enzyme or protein itself. Last I heard, evidence strongly hints that the world was an RNA (single strand) world before double stranding and then the more stable DNA double helix developed. But it's not conclusive.

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HermanCainsGhost t1_jbon0d6 wrote

The “RNA world hypothesis” was what I was taught in my upper level genetics class back in 2004, so unless I am out of the loop and it has been discarded in the 20 years since, it sounds accurate to me

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UnfinishedProjects t1_jbo8q53 wrote

I've seen this before, and I understand it, and I understand life can be created spontaneously by lightning striking in the perfect place. But what does that early early, minimal life do?? Is it about to hunt for "food"? How does it survive and replicate if it's just a few proteins that got shocked?

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Dr_Vesuvius t1_jboah5t wrote

You’re thinking of “life” as if it were a soul, some chemicals gain a “spark of life” and then they are alive.

It’s more helpful to think of life as being those things which reproduce. This isn’t a perfect definition either, of course.

You have a primordial soup full of basic organic chemicals. Some bits of RNA, some proteins, some sugars. These chemicals are already undergoing natural selection, as more stable ones survive longer, but they aren’t undergoing evolution because there is no “descent with modification”. Maybe some chemicals, through chance, form a very simple precursor to a cell which dramatically increases their survival. They can absorb small molecules while protecting themselves from the environment. Great. Does not mean they are alive. Can that structure divide into two parts which can then both grow and divide again? That’s what makes something alive.

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UnfinishedProjects t1_jbou27j wrote

You made me understand primordial soup for the first time. I mean I understood what they meant but I never thought about it being an actual soup of all the required ingredients.

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Shadver t1_jbog0eo wrote

To sort of echo the other response in a different way, I find it easier to think of early life in a chemistry sense rather than a biology sense. Chemical reactions can "reproduce"(autocatalysis), and they can compete with other reactions over the starting ingredients for the reaction. We can get these sort of lifelike qualities from very simple structures that could be outcompeted by more complex and better replicating structures over time. If you're interested in more about origin of life research, I found that the YouTube channel "Professor Dave Explains" does a really good job of giving easy enough to understand explanations for stuff like this.

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UnfinishedProjects t1_jbotuuf wrote

Okay now that actually makes perfect sense. Life is just an ongoing chemical reaction after all.

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Teslapunk1891 t1_jboeonb wrote

I find the concept of prions to be useful in understanding this. Ofc, prions are complex proteins and massively more complex and durable than any early life-precursor would have been, but they can fold other proteins into copies of themselves. Early protoliving assemblages could have been amino acid assemblages that generally tend to replicate through a few stages, and more effective/ more complicated versions of them were able to keep replicating and working together until eventually they could form something that would be considered living.

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triklyn t1_jbop8ul wrote

what does a prion do?

makes non-prions into prions. self-replication is the most important step. from there, imperfection will enable natural selection.

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danby t1_jbol01z wrote

Probably not. The last universal common ancestor (LUCA) of all life, circa 3.6 billion years ago, was bacteria-like and most likely to be free living (or somewhat colony forming). It's unlikely that a free living organism could have a genome as small as 438 genes. We also know that most major protein structural families data back to that period so a fairly complete repertoire of possible biochemical functions would have been within evolutionary reach to the LUCA. So it seems likely the LUCA was quite sophisticated from a biochemical function POV. We see that contemporary bacterial genomes tend to favour minimum levels of redundancy but that isn't the same as having smaller numbers of genes. Different types of bacterial genomes have very diverse counts of the number of genes present. Between these observations there's little reason to suspect that the LUCA's genome was minimal.

Anything older than the LUCA, such as pro-genotes (things before "modern" genomes appeared) or even earlier forms would have been substantially different to an organism with an organised genome of 438 genes. The further back in time you go towards the abiotic origin of life the more "weird" and less cellular early life probably was. There remains a reasonable chance that the earliest self replicating systems were just soups of nucleotide chains, which would arguably be the earliest life-like things on earth (circa 4.6 bya), and that's quite unlike a genome-containing cellular organism.

It remains a very open question what the earliest self-replicators that gave rise to cells might have been but all the options are pretty weird. Here's a somewhat decent summary of some models

https://www.bionity.com/en/encyclopedia/Origin_of_life.html

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ThorsTacHamr t1_jbommjb wrote

They are using this approach or a very similar one to try to find LUCA ( the lasts universal common ancestor). Not necessarily the first living thing but the oldest living thing that all current organisms can trace their lineages back to.

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danby t1_jbopbwg wrote

Minimal genome experiments generate organisms that aren't free living so they aren't really aimed at generating something like the LUCA. Mostly these experiments are trying to discover the minimal set of house keeping genes that can maintain a living cell, there's no reason to believe the LUCA was like that, nor any reason to believe that the LUCA had a minimally sized genome.

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severoon t1_jbouxw9 wrote

Also consider that "life" is likely to be an arbitrary feature in this discussion.

If you have a molecule that happens to be an enzyme which builds itself, you have yourself a self-replicating thing. Is it "alive"? Definitely not.

Well that's one feature of "life" but it's one that most people tend to think of only in the context of life. But all the features we typically think of in the context of life exist in much simpler, not-alive things.

By looking for the simplest thing we consider "alive," no matter how we define that, it's likely to end up being much simpler than what we would feel comfortable calling "life."

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