But for years, despite having these three pieces of a ribonucleotide, scientists were stumped – trying to find the circumstances under which they would merge to make a fully-formed ribonucleotide.
But science doesn’t just throw in the towel and resort to wild speculation. It keeps digging. Chemistry is complicated, and there’s usually more than one way to skin a cat.
Finally, in 2009, John Sutherland demonstrated an alternative chemical process that started with simple molecules and high-energy intermediates (many of these were also products of the Miller-Urey experiment). By simulating precipitation, evaporation, and solar irradiation they ended up with a fully formed ribonucleotide.
Now we’re getting somewhere! But how do these bond together to form become nucleic acids like RNA? Researchers Jim Ferris and Leslie Orgel discovered that ribonucleotides naturally form into strands of RNA on the surface of montmorillonite clay (a common clay found world-wide, and all over the ocean floor) when they dried and re-hydrated the sample (a process similar to the rain cycle in shallow ponds or the rise and fall of tides. Additionally, RNA strands have even been found to polymerize on simple ice crystals.
So we have strands of free-floating RNA, and polypeptide chains called proteinoids, but to get something resembling a cell, we need some type of vesicle to enclose all this.
Experiments at the Simoneit Lab simulating high-pressure/high-temperature hydrothermal vents found that fatty acids formed from hydrogen and carbon monoxide on the surface of catalytic minerals found below the ocean.
As these concentration of fatty acids build up in the water, they automatically bunched together on their own like oil droplets to form semipermeable membranes with their hydrophilic ends facing towards the water, and their hydrophobic ends turned towards each other, capturing amino acids and genetic material inside the newly formed membranes.
Inside these new little vesicles, scientists have discovered that free-floating ribonucleotides will automatically base-pair with strands of RNA with occasional mutations. They’re still trying to figure out how to get the backbone of this complimentary strand of RNA to chemically bond this new strip of ribonucleotides together without assistance. But just because we’re still looking for some pieces of this puzzle, doesn’t mean that the answer isn’t out there waiting to be uncovered.
When heated, these two complimentary strands divide, copying the protocell’s genetic material. If these strands of RNA aren’t then surrounded with a sufficiently saturated solution of nucleotides to bond with them, they can fold in on themselves forming ribozyme. These ribozymes perform different functions based on their shape which is determined by the order of nucleotides that compose them. Some ribozymes will automatically combine different amino acids together to make proteins. Others can tear proteins apart. And after examining hundreds of RNA chains, researchers at Simon Frazier University found ribozymes capable of building nucleotides from the free-floating molecules surrounding it (in other words, they could build their own building blocks)! Although initially, it did so rather poorly. But after just 10 generations of mutation and selection via PCR, ribozymes emerged that were really good at creating more nucleotides which could be used for faster replication. These ribozymes were actually involved in the process of their own replication and increased their own odds of survival.
So we now have a simple little protocell with genetic content, nucleotides, protein-making ribozymes, and a cell membrane – capable of copying its genetic content and responding to natural selection pressures. There are a lot more steps and over 3.5 billion years to get from here to modern cells, but this simple protocell is already starting to blur the boundary between life and non-life, and each step occurred automatically in simulations of early earth-like environments.
But how does this cell divide, and how can simple, single-celled prokaryotes like this evolve into complex multi-cellular eukaryotes. I’ll cover that in my next post. So make sure you’re subscribed to my mailing list so you don't miss it. And if you really like what I’m doing with this series, please consider supporting my work on a per-episode basis over on patreon.com/holykoolaid. There are different perks depending on how much you pledge per video.
- Sidney Fox Discovery of proteinoids
- The Formos Reaction by Aleksandr Butlerov
- Naturally occurring phosphate groups
- Nobel Laureate Jack Szostak's Harvard Lecture on The Origin of Cellular Life on Earth
- John Sutherland creating nucleotides
- Prebiotic synthesis of simple sugars necessary for Sutherland's experiment
- Jim Ferris and Leslie Orgel - Synthesis of RNA on montmorillonite clay
- Formation of fatty acids in hydrothermal vents
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