New Evidence on the Origins of Life on Earth

New Evidence Emerges on the Origins of Life

Hot springs and geysers at Yellowstone National Park.

Two newly published studies reveal evidence for how the genetic code developed in two distinct stages to help primordial chemicals evolve into cells.

Chapel Hill, North Carolina – In the beginning, there were simple chemicals. And they produced amino acids that eventually became the proteins necessary to create single cells. And the single cells became plants and animals. Recent research is revealing how the primordial soup created the amino acid building blocks, and there is widespread scientific consensus on the evolution from the first cell into plants and animals. But it’s still a mystery how the building blocks were first assembled into the proteins that formed the machinery of all cells. Now, two long-time University of North Carolina scientists – Richard Wolfenden, PhD, and Charles Carter, PhD – have shed new light on the transition from building blocks into life some 4 billion years ago.

Their findings, published in companion papers in the Proceedings of the National Academy of Sciences, fly in the face of the problematic “RNA world” theory, which posits that RNA – the molecule that today plays roles in coding, regulating, and expressing genes – elevated itself from the primordial soup of amino acids and cosmic chemicals to give rise first to short proteins called peptides and then to single-celled organisms.

Wolfenden and Carter argue that RNA did not work alone; in fact, it was no more likely that RNA catalyzed peptide formation than it was for peptides to catalyze RNA formation.

“Our work shows that the close linkage between the physical properties of amino acids, the genetic code, and protein folding was likely essential from the beginning, long before large, sophisticated molecules arrived on the scene,” said Carter, professor of biochemistry and biophysics at the UNC School of Medicine. “This close interaction was likely the key factor in the evolution from building blocks to organisms.”

The finding adds a new layer to the story of how life evolved billions of years ago.

Its name was LUCA

The scientific community recognizes that 3.6 billion years ago there existed the last universal common ancestor, or LUCA, of all living things presently on Earth. It was likely a single-cell organism. It had a few hundred genes. It already had complete blueprints for DNA replication, protein synthesis, and RNA transcription. It had all the basic components – such as lipids – that modern organisms have. From LUCA forward, it’s relatively easy to see how life as we know it evolved.

Before 3.6 billion years, however, there is no hard evidence about how LUCA arose from a boiling caldron of chemicals that formed on Earth after the creation of the planet about 4.6 billion years ago. Those chemicals reacted to form amino acids, which remain the building blocks of proteins in our own cells today.

“We know a lot about LUCA and we are beginning to learn about the chemistry that produced building blocks like amino acids, but between the two there is a desert of knowledge,” Carter said. “We haven’t even known how to explore it.”

The UNC research represents an outpost in that desert.

“Dr. Wolfenden established physical properties of the twenty amino acids, and we have found a link between those properties and the genetic code,” Carter said. “That link suggests to us that there was a second, earlier code that made possible the peptide-RNA interactions necessary to launch a selection process that we can envision creating the first life on Earth.”

Thus, Carter said, RNA did not have to invent itself from the primordial soup. Instead, even before there were cells, it seems more likely that there were interactions between amino acids and nucleotides that led to the co-creation of proteins and RNA.

Complexity from simplicity

Proteins must fold in specific ways to function properly. The first PNAS paper, led by Wolfenden, shows that both the polarities of the twenty amino acids (how they distribute between water and oil) and their sizes help explain the complex process of protein folding – when a chain of connected amino acids arranges itself to form a particular 3-dimensional structure that has a specific biological function.

“Our experiments show how the polarities of amino acids change consistently across a wide range of temperatures in ways that would not disrupt the basic relationships between genetic coding and protein folding,” said Wolfenden, Alumni Distinguished Professor of Biochemistry and Biophysics. This was important to establish because when life was first forming on Earth, temperatures were hot, probably much hotter than they are now or when the first plants and animals were established.

A series of biochemical experiments with amino acids conducted in Wolfenden’s lab showed that two properties – the sizes as well as the polarities of amino acids – were necessary and sufficient to explain how the amino acids behaved in folded proteins and that these relationships also held at the higher temperatures of Earth 4 billion years ago.

The second PNAS paper, led by Carter, delves into how enzymes called aminoacyl-tRNA synthetases recognized transfer ribonucleic acid, or tRNA. Those enzymes translate the genetic code.

“Think of tRNA as an adapter,” Carter said. “One end of the adapter carries a particular amino acid; the other end reads the genetic blueprint for that amino acid in messenger RNA. Each synthetase matches one of the twenty amino acids with its own adapter so that the genetic blueprint in messenger RNA faithfully makes the correct protein every time.”

Carter’s analysis shows that the two different ends of the L-shaped tRNA molecule contained independent codes or rules that specify which amino acid to select. The end of tRNA that carried the amino acid sorted amino acids specifically according to size.

The other end of the L-shaped tRNA molecule is called the tRNA anticodon. It reads codons, which are sequences of three RNA nucleotides in genetic messages that select amino acids according to polarity.

Wolfenden and Carter’s findings imply that the relationships between tRNA and the physical properties of the amino acids – their sizes and polarities – were crucial during the Earth’s primordial era. In light of Carter’s previous work with very small active cores of tRNA synthetases called Urzymes, it now seems likely that selection by size preceded selection according to polarity. This ordered selection meant that the earliest proteins did not necessarily fold into unique shapes, and that their unique structures evolved later.

Carter said, “Translating the genetic code is the nexus connecting pre-biotic chemistry to biology.”

He and Wolfenden believe that the intermediate stage of genetic coding can help resolve two paradoxes: how complexity arose from simplicity, and how life divided the labor between two very different kinds of polymers: proteins and nucleic acids.

“The fact that genetic coding developed in two successive stages – the first of which was relatively simple – may be one reason why life was able to emerge while the earth was still quite young,” Wolfenden noted.

An earlier code, which enabled the earliest coded peptides to bind RNA, may have furnished a decisive selective advantage. And this primitive system could then undergo a natural selection process, thereby launching a new and more biological form of evolution.

“The collaboration between RNA and peptides was likely necessary for the spontaneous emergence of complexity,” Carter added. “In our view, it was a peptide-RNA world, not an RNA-only world.”

The National Institutes of Health funded this work. Dr. Wolfenden holds a joint appointment in the department of chemistry in the College of Arts and Sciences at UNC-Chapel Hill.

Publications:

  • Richard Wolfenden, et al., “Temperature dependence of amino acid hydrophobicities,” PNAS, 2015; doi: 10.1073/pnas.1507565112
  • Charles W. Carter, Jr. and Richard Wolfenden, “tRNA acceptor stem and anticodon bases form independent codes related to protein folding,” PNAS, 2015; doi: 10.1073/pnas.1507569112

Image: ALAMy

23 Comments on "New Evidence on the Origins of Life on Earth"

  1. Stories like this are so cute. But sad to say, books don’t write themselves nor does DNA

    • Arnaclaudius | June 5, 2015 at 10:46 am | Reply

      DNA or RNA is not a book. The letters (A C G T/U) are metaphorical for the acid molecule chain abilities. Nothing more. Do not overstretch human imagination!

    • Don’t overstretch human imagination you say? I bet you believe in the big bang, accretion, Oort cloud, abiogenesis, macro evolution and billions of years. Insanity. Tell me about your reasoned science clown.

  2. Goodbye, Genesis; Hello reasoned science.

    • LOL. This in no way explains why it happened. Try as you might, Genesis, or otherwise. Why did they form? Be it simply RNA, or peptides-RNA, makes no difference. It still might as well be a miracle. LOL

  3. Robert Michaels | June 3, 2015 at 3:34 pm | Reply

    It’s nice when the laws of physics and biology can be removed from the equation. I bet I could come up with a better idea than those two did, if I got to “monkey” with the natural laws of the universe.. – which were created from the start..

    • Arnaclaudius | June 5, 2015 at 10:49 am | Reply

      That is the very result of laws of physics. It is called biochemistry. And it worked as you can see. No “Cells pop into existence” by gods, we have just molecule chaining according to physical laws. No miracles needed. Everything explained step by step.

      • You assume. Despite your assumption that everything is neat and tidy, you overlook the improbability of it all. LOL

        God does not play dice. LOL

  4. Charles Griffin | June 3, 2015 at 4:15 pm | Reply

    Another piece of the puzzle to the empirical reality of evolution.

  5. Jim Robertson | June 3, 2015 at 5:08 pm | Reply

    The hope that a mechanism exists to build the human DNA molecule by chance is just that.

    • Arnaclaudius | June 5, 2015 at 11:05 am | Reply

      The human DNA molecule didn’t “pop into being” like that. Not with nor without god.
      Humans do not just pop into reality. That is why miracles are not existing, nor creation exists in reality.
      The human DNA is slightly mutated primate DNA (by small microevolutionary steps), the primate DNA slightly mutated mammal DNA (by small microevolutionary steps), the mammals DNA slightly mutated synapsid DNA (by small microevolutionary steps) etc. until you reach the first cells, where DNA-Cells where slightly mutated RNA-Vessels.
      That is what the article is about.

      When you believe in popping up-higly complex human DNA out of nothing, god will not help to change this wrong believing to something meaningful. it means nothing with nor without god and also didn’t happened that way.

  6. Well, more proof that Man invented God, not God invented man. Science is wonderful. Get over it.

    • That is evidence that neanderthals existed at one time. When the Jews told Jesus that they were sons of Abraham, HE picked up some stones
      from the ground, and said: “Truly, I tell you, God can create sons for
      Abraham from these very stones.” We are spiritual beings created in God’s Holy image, we did not arise from some primordial soup.

  7. 100% opinion without a fact to prove it. Does anyone here understand that DNA is more complex than anything man has ever built?

  8. Peter Mortensen | June 4, 2015 at 7:50 am | Reply

    Even the tiniest chance of abiogenesis being possible in an existence of infinitely many planets being created through infinitely many universes will eventually yield the creation of life as we know it.

    • LMAO! 😀

      WHOA THERE! Ah, actually, you just assumed that an all-knowing God is impossible, a nd easily explained away. Then preceded to claim that an unthinking, all-powerful multi-verse creation device exists in the cosmos to create said cosmos, defying anything in-relation to thermodynamics, and heat death.

      All powerful creator? No.

      All powerful creation device with no conscience, reason, nor thought to create life?!: Makes total sense. LOL

  9. do you really believe so? need to advance further back in time…

  10. The thing about evolution that many people misunderstand is that life branches off new lines (species, genera, etc.) through the process of evolution. The populations of entire species do not simultaneously evolve into something else and the parent species does not necessarily go extinct. So, if there were “chemical machines”, if you will, that were the precursors to life that evolved along lines of what we might call “pre-life”, we would find the descendants of pre-life still going about their business even today. The pre-life would not just disappear after they’ve branched off or led to the simplest forms of what we call life – such as bacteria.

    Now, while some might suggest that the chemical conditions on the planet are no longer compatible with the supposed pre-life as an explanation for the enigma of the missing pre-life, we should expect that said pre-life should have some adaptability. Also, it is true that there are many environments of varied chemistry on the surface and underground that would improve the likelihood of pre-life environs. This enigma leads many scientists to consider exogenesis and panspermia as possible solutions. This basically means that simple forms of life arrived from elsewhere. Life then evolved into the all the complex forms of life, past and present.

    While viruses are simpler than bacteria and not considered true life, they are also not pre-life because they need life to replicate and cannot exist without life. It is therefore thought that viruses evolved from life as a kind of non-life parasite, in a sense. But, thinking along these same lines, shouldn’t life be able to evolve into pre-life? To address this question one must understand that evolution means change and not necessarily in any particular direction of complexity or otherwise. Yes, biological evolution means genetic CHANGE, only!

    Novices misunderstand that evolution can only be in the direction of more complexity. Evolution should be thought of as expansion of possibilities – in all possible directions and variations. With natural selection sorting through the myriad of possibilities mutations represent. So, if pre-life were possible, evolution should have produced it from life. The fact that there are no lifeforms or pre-life chemical machines simpler than bacterium and capable of self-replication argues that no thing that is simpler than a bacterium can faithfully replicate! This is another argument for exogenesis.

  11. Xexanoth the Progenitor | June 2, 2016 at 10:09 am | Reply

    Thank you for the well written article, and as usual please ignore the God of the Gaps types below in the comments.

  12. Cells is awfully complicated and excuse me saying so but before pondslime could create its own cells it would first have to figure out a container ie cell walls, in which to keep its DNA while it figured out how to write it out correctly.
    Blind evononsense seems perfectly acceptable to monkeys like Hawking who have no idea of how the first banana grew or what keeps a constant supply of bananas growing for them.
    Worms prove Creation is a fact.

  13. BRIAN PERPIGLIA | May 26, 2017 at 6:18 pm | Reply

    Science is proven in the lab not by the verbal gymnastics these two yahoos are trying to sell me on. You cannot get life from nonlife. Your kitchen table will not turn into your next door neighbor. The writer even takes a cheap shot at the BIBLE with his opening statement In the Beginning. The God of the BIBLE created all things. The worst tragedy of all is these two primates used taxpayer dollars to say they cannot explain from where life comes.

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