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Scientists have been working for generations to unravel the mysteries of how life began on Earth, and a once-marginal theory just gained a lot of traction.
The ‘RNA World’ theory says that the so-called primordial soup of the early Earth was filled with the single-stranded sister RNA of DNA, which carries the instructions for supporting life.
Now, a team of Salk Institute researchers has discovered a crucial piece of that puzzle and even built it in the lab: an obscure but essential class of molecules called RNA polymerase ribozymes.
The ribozymes of RNA polymerase are not well understood, but scientists now suspect that these substances made it possible for RNA to not only replicate but actually evolve in the gel and dirt of the early planet.
These scatterplots show how, over multiple rounds of evolution, new RNA polymerase ribozymes emerged. A lower quality version (top) deviated from its original sequence and tended toward randomness, while a higher quality version (bottom) retained its original function and developed new sequences.
Although little is known about RNA polymerase ribozymes, scientists know that they can copy strands of RNA.
In laboratory experiments, scientists showed that that’s not all they can do.
Apparently they can also evolve.
Their experiments showed that RNA polymerase ribozymes can not only copy RNA, but can also improve their task.
READ MORE: What is the ‘RNA World’ theory?
Life on Earth may have begun thanks to a modified version of the sister molecule of modern DNA that was integral to evolution.
RNA is structurally similar to DNA, except that one of the four building blocks, thymine, replaces uracil. This changes the shape and structure of the molecule and scientists have long believed that this chemical is the cause of the first forms of life on Earth.
Over time, they observed, the RNA polymerase ribozymes built copies of themselves and were also able to copy the RNA.
And the copies were not only functional, they actually got better at copying RNA: the same kind of evolution described by Charles Darwin.
As Darwin described evolution, the more “fit” an organism is, the more likely it is to reproduce and pass on its genetic material.
I didn’t know anything about DNA, but DNA is how genes are passed on.
The new experiment suggests that some kind of evolution may have been occurring in the RNA World scenario.
As certain RNA polymerase ribozymes got better at copying RNA, they were more likely to stick around and continue performing their role.
Those of lower quality, on the other hand, copied the RNA less reliably and their sequences drifted apart, becoming more random over multiple courses of evolution.
There may not even have been DNA to pass on, but evolution was happening, the authors of the new study said.
“We are chasing the dawn of evolution,” study lead author and Salk President Gerald Joyce said in a statement.
“By revealing these new capabilities of RNA, we are uncovering the potential origins of life itself and how simple molecules could have paved the way for the complexity and diversity of life we see today.”
He study was published in the magazine proceedings of the National Academy of Sciences.
Over time, RNA joined together to form the more familiar double-stranded structure of DNA, giving rise to single-celled organisms and then to more complex life forms.
These are all just theories, as we will never be able to go back to the origin of the planet and confirm how it all began.
But building RNA polymerase ribozymes in the lab and watching them help evolve RNA adds weight to the RNA world theory because it shows that this was theoretically possible.
The early Earth may have contained the ingredients for life long before anything existed on our planet. Scientists now have evidence that these materials could even have evolved on their own.
RNA is like the single-stranded version of DNA and contains the fragments of genetic material that cells use to communicate.
Proteins, the basic materials of living beings, are built following the instructions contained in RNA.
He is an anonymous hero of life. It’s always working and we would die without it, but DNA tends to take the credit.
“We have long wondered how simple life was in its beginnings and when it acquired the ability to begin to improve,” said the study’s first author, Nikolaos Papastavrou, a research associate in Joyce’s lab.
«This study suggests that the dawn of evolution could have been very early and very simple. Something at the level of individual molecules could sustain Darwinian evolution, and that could have been the spark that allowed life to become more complex, moving from molecules to cells and multicellular organisms.’
Some scientists claim that life arose on asteroids from the stars, while others say that the building blocks of life came from space and were assembled into life forms on Earth. An older idea holds that the basic molecules of life were assembled here on Earth from non-organic compounds.
Without RNA, most of the body’s functions would not be possible. RNA carries instructions on how to build proteins, which are the basis for almost everything cells do.
Long before animals and single-celled organisms existed, the early Earth may have harbored strands of genetic material and, more importantly, the chemicals that can cause them to replicate.
The work of Joyce and Papastavrou’s team will need to be replicated by other researchers, but for now it represents a mark in favor of a theory about how life emerged.
The team said they hope to even discover how new functions of RNA are invented through the same process of evolution.