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Biologists Replicate Key Evolutionary Step

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How RNA formed at the origins of life

Date: May 19, 2017
Source: University College London
Summary: A single process for how a group of molecules called nucleotides were made on the early Earth, before life began, has been suggested by a team of researchers.

The crux of the article.

The team demonstrated how purines and pyrimidine nucleotides can both be assembled on the same sugar scaffold to form molecules called ribonucleotides which are used to construct RNA.

Purine and pyrimidine nucleotides are used to create the DNA and RNA. The purine and pyrimidine nucleotides bind to one another through specific molecular interactions that provide a mechanism to copy and transfer information at the molecular level, which is essential for genetics, replication and evolution. Therefore understanding the origins of nucleotides is thought to be key to understanding the origins of life itself.

The team discovered that molecules, called 8-oxo-adenosine and 8-oxo-inosine, which are purine ribonucleotides, can be formed under the same chemical conditions as the natural pyrimidine ribonucleotides. They also found that one chemical precursor can divergently yield both purine and pyrimidine ribonucleotides.

"The mechanism we've reported gives both classes of molecule the same stereochemistry that is universally found in the sugar scaffold of biological nucleic acids, suggesting that 8-oxo-purine ribonucleotides may have played a key role in primordial nucleic acids," said Dr Shaun Stairs (UCL Chemistry), first author of the study.

Edited by dream_weaver

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New study sheds light on origins of life on Earth through molecular function

Date: May 17, 2017
Source: University of Illinois College of Agricultural, Consumer and Environmental Sciences
Summary:

Debate exists over how life began on Earth, but a new study provides evidence for a 'metabolism-first' model. Scientists have traced the origins and evolution of molecular functions through time. The study shows metabolism and binding arose first, followed by the functional activities of larger macromolecules and cellular machinery.

The hypothesis:

Caetano-Anollés and Ibrahim Koç, a visiting scholar in the department, found evidence for the "metabolism-first" hypothesis by studying the evolution of molecular functions in organisms representing all realms of life. For 249 organisms, their genomes -- or complete set of genes -- were available in a searchable database. What's unique about this particular resource, known as the Gene Ontology (GO) database, is the fact that for each gene product -- a protein or RNA molecule -- a set of terms describing its function goes with it.

The experiment:

The team used the information and advanced computational methods to construct a tree that traced the most likely evolutionary path of molecular functions through time. At the base of the tree, close to its roots, were the most ancient functions. The most recent were close to the crown.

The observation:

At the base of the tree, corresponding to the origin of life on Earth, were functions related to metabolism and binding. "It is logical that these two functions started very early because molecules first needed to generate energy through metabolism and had to interact with other molecules through binding," Caetano-Anollés explains.

The next major advancements were functions that made the rise of macromolecules possible, which is when RNA might have entered the picture. Next came the machinery that integrated molecules into cells, followed by the rise of functions allowing communication between cells and their environments. "Finally, as you move toward the crown of the tree, you start seeing functions related to highly sophisticated processes involving things like muscle, skin, or the nervous system," Caetano-Anolles says.

Of course if you search for and stack your molecular functions from simplest to most complex, is it a reflection of the order of chronological precedence, or a sorting based on expectation that the most ancient functions and most recent go according to the rules that were written in the computer program?

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Another article citing the RNA study two posts back on Science magazine's website:

Chemists may be zeroing in on chemical reactions that sparked the first life

. . . A handful of simple steps transformed the aldehyde into two compounds resembling adenine- and guanine-containing nucleotides, they report today in Nature Communications. The resemblance wasn’t perfect: In the base of each, a carbon atom was bound to an oxygen atom instead of a hydrogen atom as in the familiar purines.  

“It’s nice chemistry,” says Nicholas Hud, an RNA chemist at Georgia Institute of Technology in Atlanta. However, he says, that wayward oxygen atom is a key stumbling block. There’s no simple way to exchange it for hydrogen. And the unconventional purines might have been unable to form RNA analogs with the properties needed to spark life. Powner says he and his colleagues are now looking for solutions. If they succeed, the path from simple chemicals to life will be a whole lot clearer. 

 

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Did life begin on land rather than in the sea?

A paradigm-shifting hypothesis could reshape our idea about the origin of life

Date: July 18, 2017

Source: University of California - Santa Cruz

Summary: A new discovery pushes back the time for the emergence of microbial life on land by 580 million years and also bolsters a paradigm-shifting hypothesis that life began, not in the sea, but on land.

While there is still debate about whether life began on land or in the sea, the discovery of ancient microbial fossils in a place like the Pilbara shows that these geothermal areas -- full of energy and rich in the minerals necessary for life -- harbored living microorganisms far earlier than believed.

 

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