June 05, 2008

Progress in Abiogenesis: Protocells Capable of Replicating DNA Without Enzymes

This story goes in the bin marked "Woa!"

A Harvard research team led by Jack Szostack has created protocells in the laboratory made from non-living components. These very primitive, cell-like structures have an outer membrane composed of nothing more than fatty acids. The membrane can allow nucleotides to enter the cell from outside where they can be assembled into DNA without the need for the cell to synthesize any enzymes at all. It's a chemical process that probably mimics an early step in the rise of life on earth.

While we don't know for sure if this is how it all began, this discovery is at the very least a good possibility of how the first living organisms came into being based on relatively simple physical laws.

A New Way to Think About Earth's First Cells

A model protocell containing DNA; click the image for more informationA team of researchers at Harvard University have modeled in the laboratory a primitive cell, or protocell, that is capable of building, copying and containing DNA...

The protocell's fatty acid membrane allows chemical compounds, including the building blocks of DNA, to enter into the cell without the assistance of the protein channels and pumps required by today's highly developed cell membranes. Also unlike modern cells, the protocell does not use enzymes for copying its DNA.

Supported with funding from the National Science Foundation and led by Jack W. Szostak of the Harvard Medical School, the research team published its findings in the June 4, 2008, edition of the journal Nature's advance online publication...

When fatty acids are in an aqueous environment, they spontaneously arrange so that their hydrophilic, or water-loving, "heads" interact with the surrounding water molecules and their hydrophobic, or water-fearing, "tails" are shielded from the water, resulting in the formation of tiny spheres of fatty acids called micelles.

Depending upon chemical concentrations and the pH of their environment, micelles can convert into layered membrane sheets or enclosed vesicles...

When the team started its work, the researchers were not sure that the building blocks required for copying the protocell's genetic material would be able to enter the cell.

"By showing that this can happen, and indeed happen quite efficiently, we have come a little closer to our goal of making a functional protocell that, in the right environment, is able to grow and divide on its own," said Szostak...
The image below links to an animation that demonstrates how micelles (the fatty acid membranes mentioned above) are formed and change at different pHs:
Amazingly cool stuff, this. The mystery of how life began becomes less and less a mystery as time and science progress. Given a few fatty acids and some chemicals, including liquid water, it seems more likely than not that life or something very much like it is almost bound to spring up. Once there are micelles, given enough time things come into being that look a lot like your cells!

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