Theoretical origin of life; possible primordial soup (Introduction)

by David Turell , Monday, September 04, 2017, 22:40 (2423 days ago) @ David Turell

More fun and games in the lab:

https://phys.org/news/2017-09-primordial-soup-hearty-pre-protein-stew.html

"Ancestors of the first protein molecules, which are key components of all cells, could have been bountiful on pre-life Earth, according to a new study led by researchers at the Georgia Institute of Technology, who formed hundreds of possible precursor molecules in the lab. Then they meticulously analyzed the molecules with latest technology and new algorithms.

"They found that the molecules, called depsipeptides, formed quickly and abundantly under conditions that would have been common on prebiotic Earth, and with ingredients that would have likely been plentiful.

"And some of the depsipeptides evolved into new varieties in just a few days, an ability that, eons ago, could have accelerated the birth of long molecules, called peptides, that make up proteins.

***

"But complex molecules of life likely did not arise in one dramatic step that produced final products. That's the hypothesis that drives the research of Fernández and his colleagues at the NSF/NASA Center for Chemical Evolution, headquartered at Georgia Tech and based on close collaboration with the Scripps Research Institute.

"Instead, multiple easier chemical steps produced plentiful in-between products that were useful in subsequent reactions that eventually led to the first biopolymers. The depsipeptides produced in this latest study could have served as such a chemical stepping stone.

***

"To understand depsipeptides and the significance of the researchers' results, it's helpful to start by looking at peptides, which are chains of amino acids. When the chains get really long they are called polypeptides, and then proteins.

"Living cells have machinery that reads instructions in DNA on how to link up amino acids in a specific order to build very specific peptides and proteins that have functions in a living cell. For a protein to have function in a cell, its polypeptide chains have to clump up like sticky yarn to form useful shapes.

"Before cells and DNA existed on an Earth devoid of life, for polypeptides to form, amino acids had to somehow jostle together in puddles or on the banks of rivers or lakes to form chains. But peptide bonds can be tough to form, especially long chains of them.

"Other bonds, called ester bonds, form more easily, and they can link up amino acids with very similar molecules called hydroxy acids. Hydroxy acids are so much like amino acids that they can, in some cases, function as their stand-in doubles.

"The researchers mixed three amino acids with three hydroxy acids in a water solution and they formed depsipeptides, chains of amino acids and hydroxy acids held together by intermittent ester and peptide bonds. The hydroxy acids acted as an enabler to put the chains together that would have otherwise been difficult to form.

"The primordial soup may have lapped its depsipeptides onto rocks, where they dried out in the sun, then rain or dew dissolved them back into the soup, and that happened over and over. The researchers mimicked this cycle in the lab and watched as the depsipeptide chains further developed.

***

"Since ester bonds break more easily, in the experiment, the chains tended to come apart more at the hydroxy acids and hold together between the amino acids, which were connected by the stronger peptide bonds. As a result, chains could re-form and link up more and more amino acids with each other into sturdier peptides.

"In a kind of square-dance, the stand-in hydroxy acids often left their amino acid partners in the chain, and new amino acids latched onto the chain in their place, where they held on tight. In fact, a number of the depsipeptides ended up being composed almost completely of amino acids and had only remnants of hydroxy acids.

"'Now we know how peptides can form easily," Fernández said. "Next, we want to find out what's needed to get to the level of a functional protein.'" ( my bold)

Comment: These lab studies are designs that might fit what happened on Earth. My bold indicates that what they produced are far from functional proteins needed for first life. They assume amino acids were present of the correct chirality (all left handed). As usual no proof of how life might have started.