Editing Pyrimidine (section)

==Theoretical aspects==
In March 2015, [[NASA Ames]] scientists reported that, for the first time, complex [[DNA]] and [[RNA]] [[organic compound]]s of [[life]], including [[uracil]], [[cytosine]] and [[thymine]], have been formed in the laboratory under [[outer space]] conditions, using starting chemicals, such as pyrimidine, found in [[meteorite]]s. Pyrimidine, like [[polycyclic aromatic hydrocarbons]] (PAHs), the most carbon-rich chemical found in the [[universe]], may have been formed in [[red giant]]s or in [[Cosmic dust|interstellar dust]] and gas clouds.<ref name="NASA-20150303">{{cite press release |last=Marlaire |first=Ruth |title=NASA Ames reproduces the building blocks of life in laboratory |url=http://www.nasa.gov/content/nasa-ames-reproduces-the-building-blocks-of-life-in-laboratory |date=3 March 2015 |publisher=[[NASA]] |access-date=5 March 2015 }}</ref><ref name=Nuevo>{{cite journal |last1=Nuevo |first1=M.|last2=Chen |first2=Y. J.|last3=Hu |first3=W. J.|last4=Qiu |first4=J. M.|last5=Wu |first5=S. R.|last6=Fung |first6=H. S.|last7=Yih |first7=T. S.|last8=Ip |first8=W. H.|last9=Wu |first9=C. Y. R. |title=Photo-irradiation of pyrimidine in pure H<sub>2</sub>O ice with high-energy ultraviolet photons |year=2014 |journal=Astrobiology |volume=14 |issue=2|pages=119–131|url=http://www.astrochemistry.org/docs/Nuevo%202014%20H2O.pdf |doi=10.1089/ast.2013.1093|pmid=24512484|pmc=3929345|bibcode=2014AsBio..14..119N}}</ref><ref name=Sanford>{{cite book|last1=Sandford |first1=S. A. |last2=Bera |first2=P. P. |last3=Lee |first3=T. J. |last4=Materese |first4=C. K. |last5=Nuevo |first5=M. |title=Photosynthesis and photo-stability of nucleic acids in prebiotic extraterrestrial environments |date=6 February 2014 |journal=Topics of Current Chemistry |volume=356 |url=http://www.astrochemistry.org/docs/2014%20Sandford%20et%20al.-ToCC%20Chapter%20on%20Nucleobases-Ch.14.pdf |pages=123–164 |doi=10.1007/128_2013_499 |pmid=24500331 |pmc=5737941 |series=Topics in Current Chemistry |bibcode=2014ppna.book..123S |isbn=978-3-319-13271-6 }}, also published as {{cite book |chapter=14: Photosynthesis and photo-stability of nucleic acids in prebiotic extraterrestrial environments |title=Photoinduced phenomena in nucleic acids |editor1=Barbatti |editor1-first=M. |editor2=Borin |editor2-first=A. C. |editor3=Ullrich |editor3-first=S. |publisher=Springer-Verlag |location=Berlin, Heidelberg |page=499 }}</ref>

===Prebiotic synthesis of pyrimidine nucleotides===
In order to understand how [[life]] arose, knowledge is required of the chemical pathways that permit formation of the key building blocks of life under plausible [[abiogenesis|prebiotic conditions]].  The [[RNA world]] hypothesis holds that in the [[primordial soup]] there existed free-floating [[ribonucleotide]]s, the fundamental molecules that combine in series to form [[RNA]].  Complex molecules such as RNA must have emerged from relatively small molecules whose reactivity was governed by physico-chemical processes.  RNA is composed of pyrimidine and [[purine]]  nucleotides, both of which are necessary for reliable information transfer, and thus natural selection and Darwinian [[evolution]].  Becker et al. showed how pyrimidine [[nucleoside]]s can be synthesized from small molecules and [[ribose]], driven solely by wet-dry cycles.<ref>Becker S, Feldmann J, Wiedemann S, Okamura H, Schneider C, Iwan K, Crisp A, Rossa M, Amatov T, Carell T. Unified prebiotically plausible synthesis of pyrimidine and purine RNA ribonucleotides. Science. 2019 Oct 4;366(6461):76-82. doi: 10.1126/science.aax2747. PMID 31604305</ref> Purine nucleosides can be synthesized by a similar pathway.  5’-mono-and diphosphates also form selectively from phosphate-containing minerals, allowing concurrent formation of [[polynucleotide|polyribonucleotides]] with both the pyrimidine and purine bases.  Thus a reaction network towards the pyrimidine and purine RNA building blocks can be established starting from simple atmospheric or volcanic molecules.