Theoretical origin of life; RNA world won't work (Introduction)

by David Turell , Thursday, November 02, 2017, 22:40 (2578 days ago) @ David Turell

The latest papers suggest a different approach, saying RNA first doesn't work:

https://www.sciencedaily.com/releases/2017/11/171101160756.htm

"Life on Earth originated in an intimate partnership between the nucleic acids (genetic instructions for all organisms) and small proteins called peptides, according to two new papers from biochemists and biologists at the University of North Carolina at Chapel Hill and the University of Auckland. Their "peptide-RNA" hypothesis contradicts the widely-held "RNA-world" hypothesis, which states that life originated from nucleic acids and only later evolved to include proteins.

"The new papers -- 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.

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"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.

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"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.

"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, a process called translation that is essential for all life forms.

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"'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.

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"Carter and Wills developed two additional reasons why a pure RNA biology of any significance 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 cannot perform with much versatility. In particular, RNA enzymes cannot readily adjust their activities to temperature changes likely to have happened as the earth cooled, and so cannot perform the very broad range of catalytic accelerations that would have been necessary to synchronize the biochemistry of early cell-based life forms. Only peptide or protein enzymes have that kind of catalytic versatility, Carter said.

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

"'Such a rise from RNA to cell-based life would have required 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."

"Thus, because the new Carter-Wills theory actually addresses real problems of the origin of life that are concealed by the expediency of the RNA-world hypothesis, it is actually a far simpler account of how things probably happened just before life on Earth rose from the primordial soup."

Comment: Of course, life just popped up in the soup. This article is an important criticism of the RBNA world thesis, but it skips the key problem. How does life start on a rocky planet with no organic molecules that are naturally present. Not all the needed ones are shown to arrive from out space on meteorites.