Few questions have intrigued humans as much as the beginnings of life on Earth. How did the first living cells emerge? What allowed these primitive protocells to create the essential membranes necessary for cells to survive and evolve into complex organisms? Recent research has revealed a credible explanation based on the interaction of two simple molecules.
Few questions have intrigued humans as much as the beginnings of life on Earth. How did the first living cells emerge? What allowed these primitive protocells to create the essential membranes necessary for cells to survive and evolve into complex organisms?
New findings from the lab of Neal Devaraj, a Professor of Chemistry and Biochemistry at the University of California San Diego, offer a reasonable explanation involving a reaction between two basic molecules. This study has been published in Nature Chemistry.
Lipid membranes are essential for life on Earth; they form the structure of a cell, providing a space for its internal operations and supporting various biochemical reactions. While lipids are constructed from long chains of fatty acids, it remains unclear how these initial cell membranes were established from simpler molecules present on Earth billions of years ago.
Researchers believe that short-chain fatty molecules, containing fewer than 10 carbon-carbon bonds (whereas complex fatty molecules may have close to 20 bonds), were plentiful on the early Earth. Nevertheless, longer chain fatty molecules are necessary to create vesicles, which are the compartments that house a cell’s intricate machinery.
Although it’s conceivable that simple fatty molecules could spontaneously create lipid compartments, they would require concentrations that likely didn’t exist on prebiotic Earth—a time when conditions may have been suitable for life, though no life forms were present yet.
“At first glance, it may not seem groundbreaking since lipid synthesis typically requires enzymes,” noted Devaraj, who also holds the Murray Goodman Endowed Chair in Chemistry and Biochemistry. “But over four billion years ago, there were no enzymes. Yet, somehow, these primitive protocell structures emerged. What was the mechanism? That’s what we aimed to clarify.”
To investigate the origin of these early lipid membranes, Devaraj’s team began with two basic molecules: an amino acid called cysteine, and a short-chain choline thioester, which is similar to the molecules involved in the biochemical processes of fatty acid formation and breakdown.
The researchers used silica glass as a mineral catalyst, as the negatively charged silica was drawn to the positively charged thioester. On the silica surface, cysteine and thioesters naturally reacted and formed lipids, leading to the generation of membrane vesicles resembling protocells that were stable enough to support biochemical reactions. This occurred at lower concentrations compared to what would have been necessary without a catalyst.
“Part of our research involves understanding how life can arise without pre-existing life. How did that initial transition from matter to life take place?” explained Devaraj. “We have provided a potential explanation for what might have happened.”
Complete list of authors: Christy J. Cho, Taeyang An, Alessandro Fracassi, Roberto J. Brea, and Neal K. Devaraj (all from UC San Diego); Yei-Chen Lai, Alberto Vázquez-Salazar, and Irene A. Chen (all from UCLA).
This research received funding from the National Science Foundation (EF-1935372) and the National Institutes of Health (R35-GM141939).
