Theoretical origin of life: making cell walls with lipids (Introduction)

by David Turell , Friday, November 01, 2024, 20:15 (3 hours, 20 minutes ago) @ David Turell

More laboratory fun:

https://www.science.org/content/article/lab-created-protocells-provide-clues-how-life-a...

"For life to arise from Earth’s primordial ingredients, early cells needed some way to keep their contents from simply drifting away. All modern cells package their innards inside a complex, double-layered membrane made of lipids, and scientists have long wondered how the structure first coalesced from simple molecules. A study out today in Nature Chemistry offers a new recipe to explain how short lipids might have spawned the first cell membranes.

"The result is “fascinating,” says biochemist Sheref Mansy of the University of Trento, who wasn’t connected to the research. “It opens up a new avenue” for understanding how primordial cells appeared.

"Today, the main components of most cell membranes are complex, hefty molecules called phospholipids. The first cells probably relied instead on simpler lipids, possibly molecules known as fatty acids. They contain chains of carbon atoms, and versions with 10 or more carbons can spontaneously coalesce into membranes in the lab. But there’s a catch: Such lipids were probably extremely rare on early Earth.

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"Previous work from Devaraj’s lab showed the amino acid cysteine, which was also likely prevalent during our planet’s youth, can act like a chemical clamp, fastening certain precursor molecules together to yield lipids.

"In the new study, the researchers combined cysteine with chemical relatives of fatty acids containing eight carbons apiece. The amino acid reacted with the molecules, forming lipids with two tails—the phospholipids in modern membranes also sport similar double tails. Some of these lipids congregated into membrane-covered spheres known as protocells, the team reports. Although the empty compartments aren’t cells—they lack metabolism and a mechanism for heredity, among other attributes—they may mimic a stage in cellular evolution.

"The researchers noticed something else that might be relevant to the origin of the first cells: The protocells readily assembled on glass coverslips for microscope slides. Glass contains silica, as do sand and certain types of clay that would have been present on primordial Earth. Devaraj speculates the silica in such materials may have similarly sparked formation of early membranes.

"The protocells’ membranes displayed other similarities to those of genuine cells. For instance, phospholipids in modern cell membranes align themselves in a double layer. The thickness of the membranes in the researchers’ protocells suggested the lipids adopted the same arrangement. A membrane also corrals important molecules within a cell, an ability the scientists showed the protocells have as well.

"Devaraj and colleagues found that their protocells’ membranes could withstand the levels of calcium and magnesium ions likely present on primordial Earth, a key attribute as the ions are key to the function of RNA, which may have served as the earliest carrier of genetic information and the first enzymes. When the researchers outfitted the protocells with types modern RNAs that act as enzymes, the molecules catalyzed chemical reactions inside the spheres."

Comment: one must use the exact length of eight molecules each, add cysteine and get a welcome result. All of this must happen on a barren Earth by chance! Just providing a membrane without a metabolism doesn't come close to making a cell.