How did phosphate get into RNA?

August 18, 2016
Credit: Wiley

The phosphate ion is almost insoluble and is one of the most inactive of Earth's most abundant phosphate minerals. So how could phosphate have originally been incorporated into ribonucleotides, the building blocks of RNA, which are considered to be among the earliest constituents of life? American and Spanish scientists have now identified reasonable conditions to mobilize phosphate from insoluble apatite minerals for prebiotic organophosphate synthesis, including ribonucleotides. The pivotal role of urea in this process is also described in their article in the journal Angewandte Chemie.

The energy-rich organophosphate bond is one of the basic features found in modern life. Phosphoester and phosphodiester bonds are currently formed using energy from photosynthesis and the energy in our food, and are continuously degraded and reconstructed during metabolic activity within living cells. Phosphate groups also ensure the solubility of RNA and DNA molecules. But how were the very first phosphate ester bonds formed on the prebiotic Earth? Phosphate would have been mostly locked in minerals when the first nucleobases, sugars, and amino acids started life in the primeval soup, which is also known as Darwin's "warm little pond". César Menor-Salván and Nicholas V. Hud at the Georgia Institute of Technology, Atlanta, USA, and collaborators have now explored, in detail, realistic geochemical conditions that could have led to the first relevant organophosphates.

They were especially interested in the role of urea, a hydrolysis product of cyanamide and produced in Miller–Urey type reactions, which also has been shown to catalyze phosphate ester synthesis. The authors hypothesized that a eutectic mixture of urea, ammonium formate, and water could both serve as a milieu for direct phosphorylation and mobilize the phosphate of minerals, and thus allow phosphorylation from mineral sources. Additionally, upon heating formamide is formed, which is a cosolvent and could enhance phosphorylation from mineral sources. Therefore, the eutectic mixture would ensure "a consistent starting concentration of components regardless of their initial abundances," the authors wrote.

Their experiments resulted in effective phosphorylation of nucleosides when heated at moderate temperatures, provided soluble phosphate ions were available. To address the latter point, the scientists added various mixtures of ions and salts to the mixture and observed not only increased solubility of phosphate from hydroxyapatite, but also the formation of moderately soluble secondary phosphate minerals. They wrote: "These experiments suggest that an environment rich in ammonia, small organics such as urea and formate, magnesium sulfate, and could be an ideal location for prebiotic organophosphate synthesis." Every salt and ion added was very likely abundant in the environment of the prebiotic Earth. Overall, the scientists have identified realistic conditions under which early phosphorylation from insoluble sources could have taken place. So, consistent with Darwin's early thoughts: With the help of urea, phosphorylated molecules important for life can be readily formed in "warm little ponds."

Explore further: Geologists focus on mineral for clues to beginning of biological life on earth

More information: Bradley Burcar et al. Darwin's Warm Little Pond: A One-Pot Reaction for Prebiotic Phosphorylation and the Mobilization of Phosphate from Minerals in a Urea-based Solvent, Angewandte Chemie International Edition (2016). DOI: 10.1002/anie.201606239

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16 comments

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FredJose
1 / 5 (9) Aug 18, 2016
when the first nucleobases, sugars, and amino acids started life in the primeval soup,

Given that this whole article forms part of the world-wide search for the answer to how life arose from dead materials all by itself, this statement makes the rather telling assumption that it is a given fact.
Of course it is a given fact if one is predisposed to believing that there is no intelligent, all-powerful creator involved - one is simply then forced to believe that life came about from spontaneous generation.
Quite clearly the conclusion stated here is unscientific since it has not been shown yet that life can arise from dead materials, all by itself, via random chemical and physical processes, with no out side, intelligent interference[read design and construction]. Just take a look at how the researchers themselves got involved:
To address the latter point, the scientists added various mixtures of ions and salts to the mixture

What exactly does the article prove?
FredJose
1 / 5 (8) Aug 18, 2016
Given the latter action by the researchers, one can come to the simple conclusion:
Phosphate got into living DNA and RNA because the one who designed and constructed life put it there.
tinitus
Aug 18, 2016
This comment has been removed by a moderator.
cgsperling
4.4 / 5 (9) Aug 18, 2016
@FredJose

Creationists see small circles in logic where they don't exist, and then ignore the big circle in their own logic. If life cannot arise without help, Fred, then who helped your creator to arise?
snoosebaum
3 / 5 (1) Aug 18, 2016
primevil soup ?? that idea still around ? been reading Nick lane 'the vital question'
torbjorn_b_g_larsson
5 / 5 (5) Aug 18, 2016
@Fred: Of course it is an observed (not 'given') fact that life emerged on Earth, because the accreted planet was sterile hot, but now there is life. No mystery there.

But this work adds detail on *how* life emerged out of early geology.

@snoose: Sure, "prime evil" soup (as Fred the Creationist would say) may still be the consensus theory. Though some science journalists have started to claim vent theory now is, claims that so far hasn't been commented on by astrobiologists.

In any case urea/formate based solvents would be active in vents as well, the urea from Miller reactions could concentrate in alkaline hydrothermal vents and they can easily produce 2C compounds like formate.

More generally though vent environments (mid ocean ridges) are so hot that some phosphate minerals release activated pyrophosphate anyway IIRC. It is more of a problem for "pond" (pool) fresh water soup variants of soup theory.
tinitus
Aug 18, 2016
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tinitus
Aug 18, 2016
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richardwenzel987
5 / 5 (3) Aug 18, 2016
Chemical systems have degrees of complexity. Complex enough, we call them "living". Does a virus "live"? Only in a very minimal sense. It has a degree of complexity placing it in a borderline. But that borderline is only lexical. All we are dealing with is chemical systems with varying degrees of complexity. It adds nothing to call some systems living and others dead. Some are more complex and others less complex. Nothing mystical here. Life is chemistry. And there is no good a priori reason to argue that something outside of chemistry is required to account for what we are pleased to call life.
torbjorn_b_g_larsson
5 / 5 (4) Aug 20, 2016
@tinitus:

The abiotic petroleum formation theory has been widely rejected since it lacks evidence. The kerogen that turns up in various forms down to pure carbon is recycled organic.

That is because the biosphere long since captured and controls the entire carbon cycle. (One test: the pre-AGW carbon dioxide content of plant production and animal/fungus consumption.)

You could argue "but back then", but without evidence of, say, martian kerogens it is a tough sell. The current two main emergence theories, soup and vent, are if anything threatened by "tar formation" pathways.

Also, I wouldn't term oil droplet production "genetic" when biology is discussed, it confuses rather than helps.
tinitus
Aug 20, 2016
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torbjorn_b_g_larsson
5 / 5 (4) Aug 21, 2016
"The oil droplet can move, divide with inheritance or even find their way through maze for "food" in similar way, like the living animals. Therefore I consider them as an important possible link during evolution of physical systems into biological ones."

I don't kick that especially, since protein clumps and lipid micelles have been seen to do the same, and have been suggested in similar pathways several times. Even the current vent theory has a distant ancestor in observations of so called chemical gardens.

But the abiogenic petroleum formation theory has been widely rejected. You can't have oil without preexisting life.
tinitus
Aug 22, 2016
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tinitus
Aug 22, 2016
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tinitus
Aug 22, 2016
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Whydening Gyre
not rated yet Aug 22, 2016
when the first nucleobases, sugars, and amino acids started life in the primeval soup,

Given that this whole article forms part of the world-wide search for the answer to how life arose from dead materials all by itself, this statement makes the rather telling assumption that it is a given fact.
Of course it is a given fact if one is predisposed to believing that there is no intelligent, all-powerful creator involved - one is simply then forced to believe that life came about from spontaneous generation.
Quite clearly the conclusion stated here is unscientific .. Just take a look at how the researchers themselves got involved:
To address the latter point, the scientists added various mixtures of ions and salts to the mixture

What exactly does the article prove?

I'd say - more than your comment does...

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