Leaky Fat Blobs Produced Life
“How life began remains an open question,” said David Deamer in Nature,1 then filled the opening with a speculation: maybe life started in leaky blobs of fat.
The imaginary first primitive cells would have had a problem. Without transport proteins that control entrances and exits, any lucky ingredients that might have come together inside a primitive membrane might leak out. But if the membrane was too protective, the inside molecules would be trapped. “A model of a primitive cell suggests that early membranes were surprisingly permeable,” the article subtitle teased. Indeed, a team writing in the same issue published results of their laboratory simulations of an artificial vesicle that “allows small, organic ‘nutrient’ molecules to pass through its membrane.” Would that solve the problems?
Deamer switched imaginary views to a primitive earth with volcanoes popping out like acne. The“local conditions were far from equilibrium – a constant flux of energy drove organic reactions towards ever-increasing complexity,” he imagined. “This would ultimately have yielded various polymeric products, perhaps including prototypes of nucleic acids or proteins.” Next, he envisioned “vast numbers of microscopic assemblies of molecules” that became enclosed in fatty bubbles. By chance, life emerged:
In this theory of the origins of life, each cell-like assembly had a different composition from the next. Most were inert, but a few might have contained a particular mixture of components that could be driven towards further complexity by capturing energy and small ‘nutrient’ molecules from the environment – the beginnings of a heterotrophic system. As the nutrient molecules were transported into the internal compartment, they became linked together into long chains in an energy-consuming process. Life began when one or more of the assemblies found a way not only to grow, but also to reproduce by incorporating a cycle involving catalytic functions and genetic information.
The leaps in that scenario are astonishing, but finally Deamer acknowledged a problem: “the membrane that forms the compartment of the putative cell is also a permeability barrier.” How to get nutrients inside for the catalytic cycle, assuming it got going? He pointed to the work of Mansy et al in the same issue.2 They experimented with prefabricated vesicles that were able to selectively permit the passage of ribose or nucleotides but exclude polymers. The researchers “establish for the first time that a simulated prebiotic protocell can work with an external source of reagents,” he said. “a heterotrophic origin of primitive cellular life is feasible.”3
In his closing paragraph, Deamer took a swipe at the strong minority of origin-of-life researchers who believe life took hold in metabolic cycles before cells emerged: “Cells are the basic unit of all life today, and there is increasing reason to think that the first form of life was a primitive version of a cell, rather than a replicating molecule supported by a metabolic network.”
1. David Deamer, “Origins of life: How leaky were primitive cells?,” Nature 454, 37-38 (3 July 2008) | doi:10.1038/454037a.
2. Mansy et al, “Template-directed synthesis of a genetic polymer in a model protocell,” Nature 454, 122-125 (3 July 2008) | doi:10.1038/nature07018.
3. Heterotroph (other-nourished) means an organism that lives off the nutrient manufacture of others; i.e., humans are heterotrophs. Autotrophs (self-nourished) organisms make their own food. Because autotrophs, like plants, require much more complexity in order to harvest energy and make food, origin-of-life researchers have preferred to believe that the first life-forms were heterotrophs. Though the complexity gets divided up somewhat, it begs the question of how heterotrophs obtained their required nutrients with no autotrophs around.
More powerful than a loco motive, leaping tall conceptual hurdles with a single bound, faster than a speeding roulette, it’s Supermad!
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