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I understand that the current theory of chemical evolution (aka origin-of-life, abiogenesis) involves lipid-based protocells that enclosed RNA and perhaps some other compounds as a first steps to life.
I'm wondering if we see them forming today in nature, and if not, why not?
Are there successful experiments creating them in the lab? If so, what are the required conditions?
we don't think so, some parts are easy. liposomes form all the time, and can be created in lab quite easily. They quite readily encapsulate any material present when they form, including DNA. So once you have the right stuff (likely RNA) it is very easy to enclose it in a lipid bilayer.
RNA has been formed from scratch in a lab it is even easier than we thought it would be. It may form in nature today but is unlikely , the current atmosphere is very oxygen rich and bacteria are not just willing to eat RNA but also basically all the chemical building blocks as well so it is difficult to build up a concentration of the precursors in nature today.
Worse evidence of it forming today would be ridiculously difficult to demonstrate because there is a constant contamination of biologically produced RNA from decaying organisms. There is basically no place on earth today with liquid water that does not have life in it.
Here and here is a review of our current models for the origin of life, Be warned the first link is a file.There are many steps involved to get a cell but it all starts with the first molecule capable of making copies of itself.
Forming self catalysis strands in a lab would be the best evidence but has one major problems, Money. Earth had an ocean sized laboratory and millions of years to stumble one of the strands with one of the right codes through random chance (remember a self-replicating code only has to happen once) which likely could only be duplicated by doing millions or even billions of identical laboratory experiments.
Finally while the Urey-miller experiment was historically important it is by no means the best nor most modern experiment you can find much more information about the variety of experiments at this question.
There are some examples of lab-made protocells although they cannot reproduce and they die because of dilution of their components after a while.
In nature we haven't seen any, most probably because 1) nobody is looking for it and 2) even if they form they have to compete with all the other life-form, that are already optimized for that particular environment, leaving no chance of long-term survival.
In present environment the conditions are not favourable for the new type molecules /coacervates or microspheres formation because the present atmosphere is oxidizing in nature, presence of oxygen inhibits primary molecules formation. The early conditions were of reducing nature it has enormous lightning, high temperature, decaying radioactive compounds. Moreover, there were no organisms to feed on newly created molecules in water bodies . The first organisms formed on earth were Chemoheterotrophs i.e they feed on others for food and they cannot make their own food from sunlight. The first major toxic was Oxygen in gaseous form, earlier it is present in combined form or as metallic oxides in the water bodies as H2O. Now in atmosphere O2(in gaseous form) and tiny microorganism present oxidizes the the basic elements like C, NH3 to other forms like CO2. However, experiments by Miller and Oparin in-vitro conditions shows the formations of primary cells having amino acids, purines, pyrimidines - The basic requirements.
Miller and Urey proved the Chemical Evolution theory in their experiments showing the formation of many amino acids, sugars, nitrogen bases. Oparin stated that mixing large protein with a polysaccharide leads to formation of coacervates; same experiment was also done by Sydney Fox.
some of the original survive - they don't eat them all. It's not the bacteria. The abiotic factors themselves inhibit development of protocells.
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Aug 2, 2017 at 10:16
Basically the closest we've come to a living organism from scratch is an autocatylitic RNA set. Look it up.
But we haven't actually made any self contained life yet, although this video is VERY interesting.
Life can't form anymore. We have oxygen, which like Abdul said, smashes delicate primordial molecules. Also, we have an ozone layer, which stops the UV rays from hitting the earth, which as demonstrated in variants of the miller Urey experiment, were probably instrumental in the formation of life.
