Editing Miller–Urey experiment (section)

==Relevance to the origin of life==
The Miller–Urey experiment was proof that the building blocks of life could be synthesized abiotically from gases, and introduced a new prebiotic chemistry framework through which to study the origin of life. Simulations of protein sequences present in the [[last universal common ancestor]] (LUCA), or the last shared ancestor of all extant species today, show an enrichment in simple amino acids that were available in the prebiotic environment according to Miller-Urey chemistry. This suggests that the genetic code from which all life evolved was rooted in a smaller suite of amino acids than those used today.<ref name="Singh M.-2002">{{cite journal |author1=Brooks D.J. |author2=Fresco J.R. |author3=Lesk A.M. |author4=Singh M. |date=October 1, 2002 |title=Evolution of amino acid frequencies in proteins over deep time: inferred order of introduction of amino acids into the genetic code |url=http://mbe.oupjournals.org/cgi/content/full/19/10/1645 |url-status=dead |journal=Molecular Biology and Evolution |volume=19 |issue=10 |pages=1645–55 |doi=10.1093/oxfordjournals.molbev.a003988 |pmid=12270892 |archive-url=https://web.archive.org/web/20041213094516/http://mbe.oupjournals.org/cgi/content/full/19/10/1645 |archive-date=December 13, 2004 |doi-access=free}}</ref> Thus, while [[Creationism|creationist]] arguments focus on the fact that Miller–Urey experiments have not generated all 22 [[Proteinogenic amino acid|genetically-encoded amino acids]],<ref name="creation.com">{{Cite web |title=Why the Miller Urey research argues against abiogenesis |url=https://creation.com/why-the-miller-urey-research-argues-against-abiogenesis |access-date=2023-11-15 |website=creation.com |language=en-gb}}</ref> this does not actually conflict with the evolutionary perspective on the origin of life.<ref name="Singh M.-2002" />
[[File:CISS_origin_of_homochirality_conceptual_figure.jpg|left|thumb|481x481px|Conceptual figure from Ozturk and Sasselov (2022)<ref>{{Cite journal |last1=Ozturk |first1=S. Furkan |last2=Sasselov |first2=Dimitar D. |date=2022-07-12 |title=On the origins of life's homochirality: Inducing enantiomeric excess with spin-polarized electrons |journal=Proceedings of the National Academy of Sciences |language=en |volume=119 |issue=28 |pages=e2204765119 |doi=10.1073/pnas.2204765119 |doi-access=free |issn=0027-8424 |pmc=9282223 |pmid=35787048|arxiv=2203.16011 |bibcode=2022PNAS..11904765O }}</ref> of a plausible prebiotic scenario with an [[enantioselective]] bias. Irradiation of magnetized [[magnetite]] with ultraviolet light generates spin-selective electrons. The [[Helicity (particle physics)|helicity]] of the electrons leads to different [[redox reaction]] rates with different stereoisomers, leading to enantioselective products. Mechanisms like these mean that Miller-Urey and other prebiotic syntheses do not need to be enantioselective, as the environment can introduce homochirality. From: Ozturk, S.F. and Sasselov, D.D. [[doi:10.1073/pnas.2204765119|On the origins of life's homochirality: inducing enantiomeric excess with spin-polarized electrons.]] ''Proceedings of the National Academy of Sciences'' 119 (28) e2204765119 (2022). Licensed under [[CC-BY 4.0]].]]
Another common criticism is that the [[Racemic mixture|racemic]] (containing both L and D [[enantiomer]]s) mixture of amino acids produced in a Miller–Urey experiment is not exemplary of abiogenesis theories,<ref name="creation.com" /> as life on Earth today uses almost exclusively L-amino acids.<ref>Nelson, D. L., & Cox, M. M. (2017). ''Lehninger principles of biochemistry'' (7th ed.). W.H. Freeman.</ref> While it is true that Miller-Urey setups produce racemic mixtures,<ref>{{Cite journal |last1=Parker |first1=Eric T. |last2=Cleaves |first2=James H. |last3=Burton |first3=Aaron S. |last4=Glavin |first4=Daniel P. |last5=Dworkin |first5=Jason P. |last6=Zhou |first6=Manshui |last7=Bada |first7=Jeffrey L. |last8=Fernández |first8=Facundo M. |date=2014-01-21 |title=Conducting Miller-Urey Experiments |url=https://www.jove.com/t/51039/conducting-miller--urey-experiments |journal=Journal of Visualized Experiments |volume=83 |language=en |issue=83 |pages=e51039 |doi=10.3791/51039 |pmid=24473135 |pmc=4089479 |bibcode=2014JVExp..8351039P |issn=1940-087X}}</ref> the origin of [[homochirality]] is a separate area in origin of life research.<ref>{{Cite journal |last=Blackmond |first=Donna G. |date=2019 |title=The Origin of Biological Homochirality |journal=Cold Spring Harbor Perspectives in Biology |language=en |volume=11 |issue=3 |pages=a032540 |doi=10.1101/cshperspect.a032540 |issn=1943-0264|doi-access=free |pmid=30824575 |pmc=6396334 }}</ref>

Recent work demonstrates that [[Magnetism|magnetic]] mineral surfaces like [[magnetite]] can be templates for the [[enantioselective]] [[crystallization]] of chiral molecules, including [[RNA]] [[Precursor (chemistry)|precursors]], due to the [[Chirality-induced spin selectivity|chiral-induced spin selectivity (CISS)]] effect.<ref>{{Cite journal |last1=Ozturk |first1=S. Furkan |last2=Liu |first2=Ziwei |last3=Sutherland |first3=John D. |last4=Sasselov |first4=Dimitar D. |date=2023-06-09 |title=Origin of biological homochirality by crystallization of an RNA precursor on a magnetic surface |journal=Science Advances |language=en |volume=9 |issue=23 |pages=eadg8274 |doi=10.1126/sciadv.adg8274 |issn=2375-2548 |pmc=10246896 |pmid=37285423|arxiv=2303.01394 |bibcode=2023SciA....9G8274O }}</ref><ref>{{Cite journal |last1=Ozturk |first1=S. Furkan |last2=Bhowmick |first2=Deb Kumar |last3=Kapon |first3=Yael |last4=Sang |first4=Yutao |last5=Kumar |first5=Anil |last6=Paltiel |first6=Yossi |last7=Naaman |first7=Ron |last8=Sasselov |first8=Dimitar D. |date=2023-10-10 |title=Chirality-induced avalanche magnetization of magnetite by an RNA precursor |journal=Nature Communications |language=en |volume=14 |issue=1 |pages=6351 |doi=10.1038/s41467-023-42130-8 |pmid=37816811 |pmc=10564924 |arxiv=2304.09095 |bibcode=2023NatCo..14.6351O |issn=2041-1723}}</ref> Once an enantioselective bias is introduced, homochirality can then propagate through biological systems in various ways.<ref>{{Cite journal |last1=Ozturk |first1=S. Furkan |last2=Sasselov |first2=Dimitar D. |last3=Sutherland |first3=John D. |date=2023-08-14 |title=The central dogma of biological homochirality: How does chiral information propagate in a prebiotic network? |url=https://pubs.aip.org/jcp/article/159/6/061102/2905827/The-central-dogma-of-biological-homochirality-How |journal=The Journal of Chemical Physics |language=en |volume=159 |issue=6 |doi=10.1063/5.0156527 |pmid=37551802 |pmc=7615580 |arxiv=2306.01803 |bibcode=2023JChPh.159f1102O |issn=0021-9606}}</ref> In this way, enantioselective synthesis is not required of Miller-Urey reactions if other geochemical processes in the environment are introducing homochirality.

Finally, Miller-Urey and similar experiments primarily deal with the synthesis of [[monomer]]s; [[polymerization]] of these building blocks to form [[peptide]]s and other more complex structures is the next step of prebiotic chemistry schemes.<ref>{{Cite journal |last1=Pascal |first1=Robert |last2=Chen |first2=Irene A. |date=2019 |title=From soup to peptides |url=https://www.nature.com/articles/s41557-019-0318-6 |journal=Nature Chemistry |language=en |volume=11 |issue=9 |pages=763–764 |doi=10.1038/s41557-019-0318-6 |pmid=31406322 |bibcode=2019NatCh..11..763P |s2cid=199541746 |issn=1755-4349|url-access=subscription }}</ref> Polymerization requires [[condensation reaction]]s, which are thermodynamically unfavored in aqueous solutions because they expel water molecules.<ref name="Griffith-2012">{{Cite journal |last1=Griffith |first1=Elizabeth C. |last2=Vaida |first2=Veronica |date=2012-09-25 |title=In situ observation of peptide bond formation at the water–air interface |journal=Proceedings of the National Academy of Sciences |language=en |volume=109 |issue=39 |pages=15697–15701 |doi=10.1073/pnas.1210029109 |issn=0027-8424 |pmc=3465415 |pmid=22927374 |bibcode=2012PNAS..10915697G |doi-access=free }}</ref> Scientists as far back as [[J. D. Bernal|John Desmond Bernal]] in the late 1940s thus speculated that clay surfaces would play a large role in abiogenesis, as they might concentrate monomers.<ref>Tirard, S. (2011). Bernal's Conception of Origins of Life. In: Gargaud, M., ''et al.'' Encyclopedia of Astrobiology. Springer, Berlin, Heidelberg. [[doi:10.1007/978-3-642-11274-4 158|{{doi|10.1007/978-3-642-11274-4_158}}]]</ref> Several such models for mineral-mediated polymerization have emerged, such as the interlayers of [[layered double hydroxides]] like [[green rust]] over wet-dry cycles.<ref name="Erastova20172">{{cite journal |vauthors=Erastova V, Degiacomi MT, Fraser D, Greenwell HC |date=December 2017 |title=Mineral surface chemistry control for origin of prebiotic peptides |journal=Nature Communications |volume=8 |issue=1 |pages=2033 |bibcode=2017NatCo...8.2033E |doi=10.1038/s41467-017-02248-y |pmc=5725419 |pmid=29229963}}</ref> Some scenarios for peptide formation have been proposed that are even compatible with aqueous solutions, such as the hydrophobic air-water interface<ref name="Griffith-2012" /> and a novel "[[sulfide]]-mediated α-aminonitrile ligation" scheme, where amino acid precursors come together to form peptides.<ref>{{Cite journal |last1=Canavelli |first1=Pierre |last2=Islam |first2=Saidul |last3=Powner |first3=Matthew W. |date=2019 |title=Peptide ligation by chemoselective aminonitrile coupling in water |url=https://www.nature.com/articles/s41586-019-1371-4 |journal=Nature |language=en |volume=571 |issue=7766 |pages=546–549 |doi=10.1038/s41586-019-1371-4 |pmid=31292542 |s2cid=195873596 |issn=1476-4687}}</ref> Polymerization of life's building blocks is an active area of research in prebiotic chemistry.