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New View: How Life Arose on Earth

{He it is who gives life and causes death; and when He decrees a matter, He but says to it, “Be,” and it is.} [Surat Ghafir 40:68].

Causality is the natural or worldly agency or efficacy that connects the cause with the effect. The first is responsible for the second, and the second is dependent on the first.

Causation is an abstraction that indicates how the world progresses. It’s a very basic concept that it’s more apt as an explanation of other concepts of progression than as something to be explained by others more basic.

Allah Almighty has created the universe and its rules which outline how it works. God encourages us in the Holy Qur’an to search and discover these rules. {Indeed, in the creation of the heavens and the earth and the alternation of the night and the day are signs for those of understanding. Who remember Allah while standing or sitting or [lying] on their sides and give thought to the creation of the heavens and the earth, [saying], “Our Lord, You did not create this aimlessly; exalted are You [above such a thing]; then protect us from the punishment of the Fire.} [Surat Ali ‘imran 3:190-191].

Life on Earth originated in an intimate partnership between the nucleic acids and small proteins called peptides. That’s according to biologists at the University of North Carolina at Chapel Hill and the University of Auckland. Mark Derewicz of Phys.org reported on November 1.

Their “peptide-RNA” hypothesis contradicts the widely-held “RNA-world” hypothesis. The widespread theory states that life originated from nucleic acids and only later evolved to include proteins.

The new researches- one in Molecular Biology and Evolution, the other in Biosystems – show how recent experimental studies of two enzyme superfamilies surmount the tough theoretical questions about how complex life emerged on Earth more than four billion years ago.

New Thought

“Until now, some thought it’s impossible to conduct experiments to penetrate the origins of genetics,” said co-author Charles Carter, PhD, professor of biochemistry and biophysics at the UNC School of Medicine. “But we have now shown that experimental results mesh beautifully with the ‘peptide-RNA’ theory, and so these experiments provide quite compelling answers to what happened at the beginning of life on Earth.”

The special attributes of the ancestral versions of these enzyme superfamlies, and the self-reinforcing feedback system they would have formed with the first genes and proteins, would have kick-started early biology and driven the first life forms toward greater diversity and complexity, the researchers said.

Co-author Peter Wills, PhD, professor of physics at the University of Auckland, said, “Compared to the RNA-world hypothesis, what we hypothesize is much more probable scenario for the origin of life. We hope our data and the theory we’ve outlined in these papers will stimulate discussion and further research on questions relevant to the origins of life.”

The two scientists are fully aware that the RNA-world hypothesis still dominates the origin-of-life research field. “That theory is so alluring and expedient that most people just don’t think there’s any alternative,” Carter said. “But we are very confident there is.”

Before there was life on Earth, there were simple chemicals. Somehow, they produced both amino acids and nucleotides. These eventually became the proteins and nucleic acids necessary to create single cells. And the single cells became plants and animals.

Research this century has revealed how the primordial chemical soup created the building blocks of life. There is also widespread scientific consensus on the historical path by which cells evolved into plants and animals.

But it’s still a mystery how the amino acid building blocks were first assembled according to coded nucleic acid templates into the proteins that formed the machinery of all cells.

Big Debate

The widely accepted RNA-world theory posits that RNA; the molecule that plays roles in coding, regulating, and expressing genes – elevated itself from the primordial soup of amino acids and cosmic chemicals. Then, eventually it gave rise first to short proteins called peptides and then to single-celled organisms.

Carter and Wills argue that RNA couldn’t kick-start this process alone. That’s because it lacks a property they call reflexivity. It can’t enforce the rules by which it’s made. RNA needed peptides to form the reflexive feedback loop necessary to lead eventually to life forms.

At the heart of the peptide-RNA theory are enzymes so ancient and important. Their remnants still exist in all living cells. Even in some sub-cellular structures, including mitochondria and viruses. There are 20 of these ancient enzymes we call aminoacyl-tRNA synthetases (aaRSs).

Each of them recognizes one of the 20 amino acids that serve as the building blocks of proteins. (Proteins, considered the machines of life, catalyze and synchronize the chemical reactions inside cells.)

In modern organisms, an aaRS effectively links its assigned amino acid to an RNA string containing three nucleotides complementary to a similar string in the transcribed gene. The aaRSs thus play a central role in converting genes into proteins. This process is called translation that is essential for all life forms.

The 20 aaRS enzymes belong to two structurally distinct families, each with 10 aaRSs. Carter’s recent experimental studies showed that the two small enzyme ancestors of these two families were encoded by opposite, complementary strands of the same small gene. The simplicity of this arrangement, with its initial binary code of just two kinds of amino acids, suggests it occurred at the very dawn of biology.

Moreover, the tight, yin-yang interdependence of these two related but highly distinct enzymes would have stabilized early biology in a way that made inevitable the orderly diversification of life that followed.

“These interdependent peptides and the nucleic acids encoding them would have been able to assist each other’s molecular self-organization despite the continual random disruptions that beset all molecular processes,” Carter said. “We believe that this is what gave rise to a peptide-RNA world early in Earth’s history,” Carter said.

Strange Loop

Related research by Carter and UNC colleague Richard Wolfenden, PhD, previously revealed how the intimate chemistries of amino acids enabled the first aaRS enzymes to fold properly into functional enzymes, while simultaneously determining the assignments in the universal genetic coding table.

“The enforcement of the relationship between genes and amino acids depends on aaRSs. These aaRSs themselves are encoded by genes and made of amino acids,” Wills said. “The aaRSs, in turn, depend on that same relationship. There is a basic reflexivity at work here. Theorist Douglas Hofstadter called it a strange loop. We propose that this, too, played a crucial role in the self-organization of biology when life began on Earth. Hofstadter argued that reflexivity furnishes the force driving the growth of complexity.”

Carter and Wills developed two reasons why a pure RNA biology was unlikely to have predated a peptide-RNA biology. One reason is catalysis – the acceleration of chemical reactions involving other molecules.

Catalysis is a key feature of biology that RNA can’t perform with much versatility. In particular, RNA enzymes can’t readily adjust their activities to temperature changes likely to have happened as the earth cooled.

Moreover, they can’t perform the broad range of catalytic accelerations necessary to synchronize the biochemistry of cell-based life forms. Only peptide or protein enzymes have that kind of catalytic versatility, Carter said.

Final Answer!

Secondly, Wills has shown that obstacles would have blocked any transition from a pure-RNA world to a protein-RNA world and hence life.

“Rise from RNA to cell-based life require an out-of-the-blue appearance of an aaRS-like protein that worked even better than its adapted RNA counterpart,” Carter said. “That extremely unlikely event would have needed to happen not just once but multiple times; once for every amino acid in the existing gene-protein code. It just doesn’t make sense.”


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