Monday, 16 November 2020

Evolution News - Closing Creationism's Abiogenesis God-Shaped Gap

Early Earth (Artist's impression)

Credit: NASA's Goddard Space Flight Center Conceptual Image Lab
Cysteine synthesis was a key step in the origin of life | UCL News - UCL – University College London

Abiogenesis is the creation industry's favourite fall-back gap for when they find the evidence for evolution irrefutable and overwhelming. Science is then challenged to reproduce a fully functional complex cell in a laboratory, starting out with a few raw chemicals.

What they've been conditioned to believe is that any current gap in our scientific knowledge will, unlike all the previous gaps, never be closed, so it must be done by a god, notwithstanding the absurd false dichotomy in that argument.

So, these instances of their abiogenesis god-shaped gap shrinking considerably under scientific scrutiny is bound to produce hand-waving denialism in even the hardiest of creationists. It is, of course just another small step by science toward a comprehensive understanding of how self-replicating, entropy-managing, free-living collections of chemicals in a bag, started evolving into today's amazing biodiversity.

As the UCL press release explains:
In an important step during the early evolution of life on Earth, the formation of the amino acid cysteine delivered vital catalysts, which enabled the earliest protein molecules to form in water, according to a new study by UCL researchers.

All proteins are built from the same 20 amino acids. One of these, cysteine, was assumed not to have been present at the origin of life. Despite its fundamental importance to all life today, it was unclear how cysteine might have formed on the early Earth.

In a new study, published in Science, UCL scientists have recreated how cysteine was formed at the origins of life. Additionally, they have observed how, once formed, cysteine catalyses the fusion of peptides in water – a fundamental step in the path towards protein enzymes.

The UCL researchers created cysteine using very simple chemistry and chemicals – hydrogen cyanide and hydrogen sulfide – that were likely to be abundant on the early Earth. The route that they have unravelled closely resembles how cysteine is synthesised in living organisms today, and the researchers believe they are historically linked.

The study also found that cysteine residues catalyse peptide synthesis in water by joining together short peptide fragments that the team had previously found in a study published in Nature last year.

Co-lead author and Research Fellow Dr Saidul Islam (UCL Chemistry) said: “We have shown that nitriles possess the in-built energy required to form peptide bonds in water. This is the simplest way of making peptides that works with all of the 20 amino acids, which makes it all the more incredible.

“It is precisely the sort of simple, yet special, chemistry that was essential to kick-start life several billion years ago. Our study provides further evidence that the molecules of life descended from nitrile chemistry on the early Earth.”

Co-lead author Dr Callum Foden, who completed the work while a PhD student at UCL, said: “The peptide synthesis we discovered is simple, highly selective and uses molecules that were available on the early Earth.

“A single cysteine residue is enough to produce robust catalytic activity. It is remarkable that such small molecules can carry out such an important (bio)chemical reaction, selectively in water, at neutral pH, and in such high yields.”
The team's findings are published in Nature:

Abstract

Peptide biosynthesis is performed by ribosomes and several other classes of enzymes, but a simple chemical synthesis may have created the first peptides at the origins of life. α-Aminonitriles—prebiotic α–amino acid precursors—are generally produced by Strecker reactions. However, cysteine’s aminothiol is incompatible with nitriles. Consequently, cysteine nitrile is not stable, and cysteine has been proposed to be a product of evolution, not prebiotic chemistry. We now report a high-yielding, prebiotic synthesis of cysteine peptides. Our biomimetic pathway converts serine to cysteine by nitrile-activated dehydroalanine synthesis. We also demonstrate that N-acylcysteines catalyze peptide ligation, directly coupling kinetically stable—but energy-rich—α-amidonitriles to proteinogenic amines. This rare example of selective and efficient organocatalysis in water implicates cysteine as both catalyst and precursor in prebiotic peptide synthesis.

No doubt to the consternation of creationists, a relatively simple and easy chemical reaction could easily have given rise to a catalyst capable of producing high yields of amino acid chains - the precursors of essential enzymes - in the conditions that would have been common on early Earth a simple, neutral pH aqueous solution of common inorganic chemicals.

The traditional response of creationists is now to move the goal-posts and demand that science produces something else happening that no-one claims ever happened.







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