Structure that links amino acids suggests that early organisms could have been based on an RNA–protein mix.
Chemists say they have solved a crucial problem in a theory of life’s beginnings, by demonstrating that RNA molecules can link short chains of amino acids together.
Credit: Omikron/Science Photo Library
The findings, published on 11 May in Nature1, support a variation on the ‘RNA world’ hypothesis, which proposes that before the evolution of DNA and the proteins it encodes, the first organisms were based on strands of RNA, a molecule that can both store genetic information — as sequences of the nucleosides A, C, G and U — and act as a catalyst for chemical reactions.
The discovery “opens up vast and fundamentally new avenues of pursuit for early chemical evolution”, says Bill Martin, who studies molecular evolution at Heinrich Heine University Düsseldorf in Germany.
Chemists say they have solved a crucial problem in a theory of life’s beginnings, by demonstrating that RNA molecules can link short chains of amino acids together.
The findings, published on 11 May in Nature1, support a variation on the ‘RNA world’ hypothesis, which proposes that before the evolution of DNA and the proteins it encodes, the first organisms were based on strands of RNA, a molecule that can both store genetic information — as sequences of the nucleosides A, C, G and U — and act as a catalyst for chemical reactions.
The discovery “opens up vast and fundamentally new avenues of pursuit for early chemical evolution”, says Bill Martin, who studies molecular evolution at Heinrich Heine University Düsseldorf in Germany.
“This is a very exciting finding,” says Martin, “not only because it maps out a new route to RNA-based peptide formation, but because it also uncovers new evolutionary significance to the naturally occurring modified bases of RNA.” The results point to an important part played by RNA at the origins of life, but without requiring RNA alone to self-replicate, Martin adds.
To show that this is a plausible origin of life, scientists must complete several further steps. The peptides that form on the team’s RNA are composed of a random sequence of amino acids, rather than one determined by information stored in the RNA. Carell says that larger RNA structures could have sections that fold into shapes that ‘recognize’ specific amino acids at specific sites, producing a well-determined structure. And some of these complex RNA–peptide hybrids could have catalytic properties, and be subject to evolutionary pressure to become more efficient. “If the molecule can replicate, you have something like a mini organism,” says Carell.
Nature
It is apparent from the article that researcher intervention was critical in obtaining the reported outcome. Also, the pre-existence of complex, functional biomolecules is assumed (RNA itself, and ribosomes consisting of RNA segments and proteins). Evolution is mentioned several times as a means of guiding the nascent process into a fully self-replicating “mini organism.” Wishful thinking cannot overturn the information-barrier challenges involved in producing functional, self-replicating biomolecular machinery.