from the start-your-life-with-a-glass-of-fruit-juice dept.
Chemists have found a series of chemical reactions that could have led to the first life on Earth:
Chemists at The Scripps Research Institute (TSRI) have developed a fascinating new theory for how life on Earth may have begun. Their experiments, described today in the journal Nature Communications, demonstrate that key chemical reactions that support life today could have been carried out with ingredients likely present on the planet four billion years ago.
[...] For the new study, Krishnamurthy and his coauthors, who are all members of the National Science Foundation/National Aeronautics and Space Administration Center for Chemical Evolution, focused on a series of chemical reactions that make up what researchers refer to as the citric acid cycle.
[...] Leaders of the new study started with the chemical reactions first. They wrote the recipe and then determined which molecules present on early Earth could have worked as ingredients. The new study outlines how two non-biological cycles—called the HKG cycle and the malonate cycle—could have come together to kick-start a crude version of the citric acid cycle. The two cycles use reactions that perform the same fundamental chemistry of a-ketoacids and b-ketoacids as in the citric acid cycle. These shared reactions include aldol additions, which bring new source molecules into the cycles, as well as beta and oxidative decarboxylations, which release the molecules as carbon dioxide (CO2).
As they ran these reactions, the researchers found they could produce amino acids in addition to CO2, which are also the end products of the citric acid cycle. The researchers think that as biological molecules like enzymes became available, they could have led to the replacement of non-biological molecules in these fundamental reactions to make them more elaborate and efficient.
Linked cycles of oxidative decarboxylation of glyoxylate as protometabolic analogs of the citric acid cycle (open, DOI: 10.1038/s41467-017-02591-0) (DX)
Previously: Diamidophosphate (DAP): "Missing Link" for Abiogenesis? (also by The Scripps Research Institute)
Related: Did Life on Earth Start Due to Meteorites Splashing Into Warm Little Ponds?
Life's First Molecule Was Protein, Not RNA, New Model Suggests
Analysis of Microfossils Finds that Microbial Life Existed at Least 3.5 Billion Years Ago
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Life on Earth began somewhere between 3.7 and 4.5 billion years ago, after meteorites splashed down and leached essential elements into warm little ponds, say scientists at McMaster University and the Max Planck Institute in Germany. Their calculations suggest that wet and dry cycles bonded basic molecular building blocks in the ponds' nutrient-rich broth into self-replicating RNA molecules that constituted the first genetic code for life on the planet.
The researchers base their conclusion on exhaustive research and calculations drawing in aspects of astrophysics, geology, chemistry, biology and other disciplines. Though the "warm little ponds" concept has been around since Darwin, the researchers have now proven its plausibility through numerous evidence-based calculations.
[...] The spark of life, the authors say, was the creation of RNA polymers: the essential components of nucleotides, delivered by meteorites, reaching sufficient concentrations in pond water and bonding together as water levels fell and rose through cycles of precipitation, evaporation and drainage. The combination of wet and dry conditions was necessary for bonding, the paper says.
Original URL: Did life on Earth start due to meteorites splashing into warm little ponds?
Origin of the RNA world: The fate of nucleobases in warm little ponds (DOI: 10.1073/pnas.1710339114) (DX)
-- submitted from IRC
From Quanta Magazine: Life's First Molecule Was Protein, Not RNA, New Model Suggests
Proteins have generally taken a back seat to RNA molecules in scientists' speculations about how life on Earth started. Yet a new computational model that describes how early biopolymers could have grown long enough to fold into useful shapes may change that. If it holds up, the model, which is now guiding laboratory experiments for confirmation, could re-establish the reputation of proteins as the original self-replicating biomolecule.
For scientists studying the origin of life, one of the greatest chicken-or-the-egg questions is: Which came first — proteins or nucleic acids like DNA and RNA? Four billion years ago or so, basic chemical building blocks gave rise to longer polymers that had a capacity to self-replicate and to perform functions essential to life: namely, storing information and catalyzing chemical reactions. For most of life's history, nucleic acids have handled the former job and proteins the latter one. Yet DNA and RNA carry the instructions for making proteins, and proteins extract and copy those instructions as DNA or RNA. Which one could have originally handled both jobs on its own?
For decades, the favored candidate has been RNA — particularly since the discovery in the 1980s that RNA can also fold up and catalyze reactions, much as proteins do. Later theoretical and experimental evidence further bolstered the "RNA world" hypothesis that life emerged out of RNA that could catalyze the formation of more RNA.
But RNA is also incredibly complex and sensitive, and some experts are skeptical that it could have arisen spontaneously under the harsh conditions of the prebiotic world. Moreover, both RNA molecules and proteins must take the form of long, folded chains to do their catalytic work, and the early environment would seemingly have prevented strings of either nucleic acids or amino acids from getting long enough.
Scientists Just Found a Vital Missing Link in The Origins of Life on Earth
Researchers from The Scripps Research Institute in California have identified a molecule capable of performing phosphorylation in water, making it a solid candidate for what has until now been a missing link in the chain from lifeless soup to evolving cells. In the classic chicken and egg conundrum of biology's origins, debate continues to rage over which process kicked off others in order to get to life. Was RNA was[sic] followed by protein structures? Did metabolism spark the whole shebang? And what about the lipids?
No matter what school of abiogenesis you hail from, the production of these various classes of organic molecules requires a process called phosphorylation – getting a group of three oxygens and a phosphorus to attach to other molecules.
Nobody has provided strong evidence in support of any particular agent that might have been responsible for making this happen to prebiotic compounds. Until now. "We suggest a phosphorylation chemistry that could have given rise, all in the same place, to oligonucleotides, oligopeptides, and the cell-like structures to enclose them," says researcher Ramanarayanan Krishnamurthy.
Enter diamidophosphate (DAP). Combined with imidazole acting as a catalyst, DAP could have bridged the critical gap from early compounds such as uridine and cytidine. That might not seem overly exciting, but phosphorylating nucleosides like these is a crucial step on the road to building the chains of RNA that could serve as the first primitive genes.
Also at Newsweek. Diamidophosphate.
Phosphorylation, oligomerization and self-assembly in water under potential prebiotic conditions (DOI: 10.1038/nchem.2878) (DX)
Related: Life's First Molecule Was Protein, Not RNA, New Model Suggests
According to a new fossil analysis, previously described Australian fossils do contain evidence of 3.5-billion-year-old microbial life. However, the complexity of the fossilized microbes suggests that life arose much earlier, possibly as far back as 4 billion years ago:
In 1992, researchers discovered evidence of what was then potentially the earliest life on Earth: 3.5-billion-year-old microscopic squiggles encased in Australian rocks. Since then, however, scientists have debated whether these imprints truly represent ancient microorganisms, and even if they do, whether they're really that old. Now, a comprehensive analysis of these microfossils suggests that these formations do indeed represent ancient microbes, ones potentially so complex that life on our planet must have originated some 500 million years earlier.
The new work indicates these early microorganisms were surprisingly sophisticated, capable of photosynthesis and of using other chemical processes to get energy, says Birger Rasmussen, a geobiologist at Curtin University in Perth, Australia, who was not involved with the work. The study "will probably touch off a flurry of new research into these rocks as other researchers look for data that either support or disprove this new assertion," adds Alison Olcott Marshall, a geobiologist at the University of Kansas in Lawrence who was not involved in the effort.
[...] The analysis detected several distinct carbon ratios in the material [DOI: 10.1073/pnas.1718063115] [DX], Schopf, Valley, and colleagues report today in the Proceedings of the National Academy of Sciences. Two types of microfossils had the same carbon ratio as modern bacteria that use light to make carbon compounds that fuel their activities—a primitive photosynthesis that did not involve oxygen. Two other types of microfossils had the same carbon ratios as microbes known as archaea that depend on methane as their energy source—and that played a pivotal role in the development of multicellular life. The ratio of a final type of microfossil indicated that this organism produced methane as part of its metabolism.
That there are so many different carbon ratios strengthens the case that these are real fossils, Schopf says. Any inorganic processes that could have created the squiggles would be expected to leave a uniform carbon ratio signature, he says. The fact that microbes were already so diverse at this point in Earth's history also suggests that life on our planet may date back to 4 billion years ago, he says. Other researchers have found signs of life dating back at least that far, but those findings are even more controversial than Schopf's.
Also at University of Wisconsin-Madison.
Previously: Ancient Rocks Record First Evidence for Photosynthesis That Made Oxygen
3.7 Billion-Year-Old Fossil Found
Oldest Evidence of Life on Earth Found in 3.77-4.28 Billion Year Old Fossils
Earliest Known Evidence for Microbial Life on Land: 3.48 Billion Years Old
(Score: 0) by Anonymous Coward on Tuesday January 09 2018, @05:20PM
Orange swamp beings. Now where have I heard that before?
(Score: 2) by linkdude64 on Tuesday January 09 2018, @06:36PM (3 children)
Zapping these chemicals and blending them together in tanks until RNA appears or something?
"demonstrate that key chemical reactions that support life today could have been carried out with ingredients likely present on the planet four billion years ago."
Wouldn't this appear to be the case given life on the planet exists? I assume these same chemicals would have been present 3 billion years ago as well. And 30 minutes ago. Or is this an exclusive statement, where these chemicals only existed on earth for a given period in our history? Obviously I didn't read TFA.
(Score: 0) by Anonymous Coward on Tuesday January 09 2018, @08:18PM
The enzymes that catalyze the reactions definitely did not exist back then.
(Score: 0) by Anonymous Coward on Tuesday January 09 2018, @09:09PM
I think what they meant was that these would have existed in the absence of life.
(Score: 2) by hendrikboom on Tuesday January 09 2018, @10:55PM
"demonstrate that key chemical reactions that support life today could have been carried out with ingredients likely present on the planet four billion years ago."
Yes, that's obvious, assuming the hypothesis that life originated on earth instead of being transplanted here, as some suspect.
Consider this a data point in the direction of confirming the hypothesis,