Scientists at Penn State are using polymers to uncover clues as to how cellular life on Earth 4 billion years ago may have formed.
Ribonucleic acid (RNA) — long strands of molecules that catalyze biological reactions in cells and control gene expression — preceded the appearance of DNA, according to an “RNA-world hypothesis.” Unlike DNA, which helps build proteins and therefore building blocks of life, RNA can have many different molecular conformations and is interactive, reports R&D Magazine.
But in the RNA-world hypothesis, there is a missing piece of the puzzle. That is what the researchers at Penn State — two professors of chemistry, Christine Keating and Philip Bevilacqua, and two graduate students, Christopher Strulson and Rosalynn Molden — tried to resolve.
It’s not enough to have the necessary molecules that make up RNA floating around; they need to be compartmentalized and they need to stay together without diffusing away. This packaging needs to happen in a small-enough space — something analogous to a modern cell — because a simple fact of chemistry is that molecules need to find each other for a chemical reaction to occur.
Today, lipid-like molecules comprise cellular membranes. But those membranes did not exist billions of years ago. To find out how early cell-like structures could have been farmed and acted to bring the RNA together, Strulson and Molden made the “packaging.”
“Our team prepared compartments using solutions of two polymers called polyethylene glycol (PEG) and dextran,” Keating explains. “These solutions form distinct polymer-rich aqueous compartments, into which molecules like RNA can become locally concentrated.”
The researchers found that once the RNA was concentrated into the dextran-rich compartments, the RNA molecules associated physically, creating chemical reactions. “Interestingly, the more densely the RNA was packed, the more quickly the reactions occurred,” Bevilacqua explains.
The team acknowledges that PEG and dextran were probably not the specific polymers present on Earth eons ago that started RNA’s chemistry. But they provide a reasonable explanation as to how compartmentalization-phase separation could have occurred.
“The aqueous-phase compartments we manufactured using dextran and PEG can drive biochemical reactions by increasing local reactant concentrations,” Keating says. “So, it’s possible that some other sorts of polymers might have been the molecules that drove compartmentalization on the early Earth.”
The scientists want to continue their model-cell research using other polymers. Keating says:
We are interested in looking at compartmentalization in polymer systems that are more closely related to those that may have been present on the early Earth, and also those that may be present in contemporary biological cells, where RNA compartmentalization remains important for a wide range of cellular processes.
Source: “Researchers study formation of early cellular life,” R&D Magazine, 10/15/12
Image by C. A. Strulson, Penn State University, used with permission.
Dale McGeehon has been a journalist and editor for more than 25 years, covering chemical regulation and testing for Pesticides and Toxic Chemical News and innovations in material sciences for the National Technology Transfer Center. His writing credits include Omni and College Park magazines and The New York Times.