About 4 billion years ago, Earth started developing the right ingredients for life. Scientists who study how life began wonder what chemicals were present back then. They want to know if the chemistry of early Earth was anything like what living things need today.

They do know that spherical blobs of fats called protocells came before modern cells. But how did the first protocells form? And how did they change chemically to create different types of life?

Now, scientists have found a plausible way that protocells could have formed and evolved. Their discovery was published in the journal Chem.

The findings suggest that a chemical process called phosphorylation happened earlier than expected. That’s when phosphate groups get added to a molecule. This would have made the first simple protocells into more complex double-chained structures. Those structured protocells could then host chemical reactions and divide to make new protocells with all kinds of functions.

By revealing how protocells formed, scientists can better grasp how early life may have evolved. As the study’s lead author, Ramanarayanan Krishnamurthy, says: At some point, we all wonder where we come from. Now we’ve found a plausible way that phosphates could have gotten incorporated into cell-like structures sooner than thought. This sets the stage for life.

Krishnamurthy and his team study what chemical processes created the simple substances and structures present on prebiotic Earth before life began. They wanted to see if phosphates, which aid almost every chemical reaction in the body today, were involved in making protocells back then.

The scientists suspected protocells first formed from fatty acids. But they didn’t know how protocells went from a single chain to more stable double chains with phosphates. That’s what allows them to host chemical reactions inside.

To solve this mystery, the researchers tried to mimic plausible prebiotic conditions in the lab. They mixed together chemicals like fatty acids and glycerol that may have existed on early Earth. Glycerol is a common byproduct of soap production. Then they watched to see what reactions occurred and added other chemicals to make new combinations.

They repeatedly cooled and heated the solutions overnight, shaking them gently to encourage reactions. Next, they used fluorescent dyes to check each mixture for vesicle formation. Vesicles are spherical, cell-like structures made of lipids. In some trials, the scientists varied the pH, ratios of ingredients and other factors. This helped them understand what controlled vesicle formation.

The vesicles were able to transition from a fatty acid environment to a phospholipid one during our experiments, says lead author Sunil Pulletikurti. This suggests early Earth had chemistry that could support this.

It turns out the fatty acids and glycerol may have undergone phosphorylation to create that more stable double-chain structure. Specifically, fatty acid esters derived from glycerol can form vesicles with differing tolerances of metal ions, temperatures and pH. This is a critical step in the evolution of diversity.

As collaborator Ashok Deniz says: We have uncovered a plausible pathway of how phospholipids could have emerged during this evolving chemical process. It’s exciting to learn how the earliest chemicals may have changed to enable life on Earth.


Sources

The Scripps Research Institute | Sunil Pulletikurti, Kollery S. Veena, et al., Experimentally modeling the emergence of prebiotically plausible phospholipid vesicles. Chem, doi.org/10.1016/j.chempr.2024.02.007


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