Earth is estimated to be about 4.5 billion years old, and for much of that history, it has been home to life in one weird form or another.
How life formed on Earth is still a mystery.
Some scientists think life appeared the moment our planet’s environment was stable enough to support it.
Another examination offers proof that the first building blocks may have matched their environment, beginning messier than previously suspected.
Life is built with three major components: RNA, DNA, and proteins. RNA and DNA are genetic codes that program how to run and reproduce cells, and proteins carry out their instructions.
The first cell that originated on earth had all these three pieces. By the time they grew and replicated, competing in Darwin’s game to create the diversity of life today: bacteria, fungi, wolves, whales, and humans.
According to a theory called ‘RNA World hypothesis,’ RNA, unlike DNA, can self-replicate, that molecule may have come first. But, recent researches have suggested that the molecule’s nucleotides—the A, C, G, and U that form its backbone—could have formed from chemicals available on early Earth.
Jack Szostak, a Nobel Prize Laureate, professor of chemistry and chemical biology and genetics at Harvard University, said, “Years ago, the naive idea that pools of pure concentrated ribonucleotides might be present on the primitive Earth was mocked by Leslie Orgel as ‘the Molecular Biologist’s Dream. But how relatively modern homogeneous RNA could emerge from a heterogeneous mixture of different starting materials was unknown.”
A new study presented a new model to know how RNA could have emerged. For this, scientists started by proposing a Frankenstein-like beginning, with RNA growing out of a mixture of nucleotides with similar chemical structures: arabino- deoxy- and ribonucleotides (ANA, DNA, and RNA).
In the Earth’s chemical melting pot, it’s far-fetched that an ideal version of RNA formed consequently. Numerous versions of nucleotides converged to form patchwork molecules with bits of both modern RNA and DNA, and also mostly defunct genetic molecules, for example, ANA. These chimeras, like the monstrous hybrid lion, eagle, and serpent creatures of Greek mythology, may have been the first steps toward today’s RNA and DNA.
Seohyun Kim, a postdoctoral researcher in chemistry and first author on the paper, said, “Modern biology relies on relatively homogeneous building blocks to encode genetic information. So, if Szostak and Kim are right and Frankenstein molecules came first, why did they evolve to homogeneous RNA?”
Kim put them to the test: He pitted potential primordial hybrids against modern RNA, manually copying the chimeras to imitate the process of RNA replication. Pure RNA, he found, is just better—more efficient, more precise, and faster—than its heterogeneous counterparts. In another surprising discovery, Kim found that the chimeric oligonucleotides—like ANA and DNA—could have helped RNA evolve the ability to copy itself.
He said, “Intriguingly, some of these variant ribonucleotides are compatible with or even beneficial for the copying of RNA templates.”
Scientists noted, “If the more efficient early version of RNA reproduced faster than its hybrid counterparts, then, over time, it would out-populate its competitors. Hybrids grew into modern RNA and DNA, which then outpaced their ancestors and, eventually, took over.”
Szostak said, “No primordial pool of pure building blocks was needed. The intrinsic chemistry of RNA copying chemistry would result, over time, in the synthesis of increasingly homogeneous bits of RNA. The reason for this, as Seohyun has so clearly shown, is that when different kinds of nucleotides compete for the copying of a template strand, it is the RNA nucleotides that always win. It is RNA that gets synthesized, not any of the related kinds of nucleic acids.”
The study is published in the Journal of the American Chemical Society.