Editing Guanine (section)

==Other occurrences and biological uses==
The word guanine derives from the Spanish loanword {{lang|es|guano}} ('bird/bat droppings'), which itself is from the [[Quechua language|Quechua]] word {{lang|qu|wanu}}, meaning 'dung'. As the [[Oxford English Dictionary]] notes, guanine is "A white amorphous substance obtained abundantly from guano, forming a constituent of the excrement of birds".<ref>OED. "guanine" and also "guano".</ref>

In 1656 in Paris, a Mr. Jaquin extracted from the scales of the fish [[Common bleak|''Alburnus alburnus'']] so-called "pearl essence",<ref>Johann Rudolf von Wagner, Ferdinand Fischer, and L. Gautier, ''Traité de chimie industrielle'' (Treatise on industrial chemistry), 4th ed., (Paris, France:  Masson & Co., 1903), vol. 2, [https://books.google.com/books?id=K2mhGDwiSJsC&pg=PA64 pp. 64–65.]</ref> which is crystalline guanine.<ref>In 1861 the French chemist [[Charles-Louis Barreswil]] (1817–1870) found that "pearl essence" was guanine.  See:  Barreswil (1861) [http://gallica.bnf.fr/ark:/12148/bpt6k3010v/f246.item.zoom "Sur le blanc d'ablette qui sert à la fabrication des perles fausses"] (On the white of ablette that's used in making imitation pearls), ''Comptes rendus'', '''53''' :  246.</ref> In the cosmetics industry, crystalline guanine is used as an additive to various products (e.g., shampoos), where it provides a pearly [[iridescence|iridescent]] effect. It is also used in metallic paints and simulated pearls and plastics. It provides shimmering luster to eye shadow and [[nail polish]]. Facial treatments using the droppings, or guano, from Japanese nightingales have been used in Japan and elsewhere, because the guanine in the [[Uguisu no fun|dropping]]s makes the skin look paler.<ref>{{cite web |title=Geisha facial, the 'latest beauty secret' of Victoria Beckham, brought to the masses |last=Whitworth |first=Melissa |date=2008-10-16 |access-date=2008-11-20 |url=https://www.telegraph.co.uk/fashion/beauty/3365670/Geisha-facial%2C-the-%27latest-beauty-secret%27-of-Victoria-Beckham%2C-brought-to-the-masses.html |archive-url=https://web.archive.org/web/20081205010654/http://www.telegraph.co.uk/fashion/beauty/3365670/Geisha-facial%2C-the-%27latest-beauty-secret%27-of-Victoria-Beckham%2C-brought-to-the-masses.html |url-status=dead |archive-date=2008-12-05 |publisher=Telegraph |work=Lifestyle}}</ref> Guanine crystals are rhombic platelets composed of multiple transparent layers, but they have a high [[Refractive index|index of refraction]] that partially reflects and transmits light from layer to layer, thus producing a pearly luster. It can be applied by spray, painting, or dipping. It may irritate the eyes. Its alternatives are [[mica]], faux pearl (from ground shells),<ref>{{cite journal |title=How Pearls are Made...Faux, Fake, Imitation, Simulated or Man-made |url=http://www.karipearls.com/how-pearls-are-made.html}}</ref> and [[aluminium]] and [[bronze]] particles.

Guanine has a very wide variety of biological uses that include a range of functions ranging in both complexity and versatility. These include camouflage, display, and vision among other purposes.<ref name=":0" />

Spiders, scorpions, and some amphibians convert ammonia, as a product of protein metabolism in the cells, to guanine, as it can be excreted with minimal water loss.<ref name=":0">{{Cite journal |date=2017 |title=Light manipulation by guanine crystals in organisms: biogenic scatterers, mirrors, multilayer reflectors and photonic crystals |journal=Advanced Functional Materials |volume=27 |issue=6 |page=1603514 |doi=10.1002/adfm.201603514 |last1=Gur |first1=Dvir |last2=Palmer |first2=Benjamin A. |last3=Weiner |first3=Steve |last4=Addadi |first4=Lia |s2cid=136383728 }}</ref>

Guanine is also found in specialized skin cells of fish called [[iridocyte]]s (e.g., the [[sturgeon]]),<ref name="fox"/><ref name=":0" /> as well as being present in the reflective deposits of the eyes of [[deep-sea fish]] and some [[reptile]]s, such as [[crocodile]]s and [[chameleon]]s.<ref name="fox">{{cite book |last=Fox |first=D.L. |year=1979 |title=Biochromy, natural coloration of living things |publisher=University of California Press |isbn=978-0-520-03699-4}}</ref>

On 8 August 2011, a report, based on [[NASA]] studies with [[meteorites]] found on Earth, was published suggesting building blocks of DNA and RNA (guanine, [[adenine]] and related [[organic molecules]]) may have been formed extra-terrestrially in outer space.<ref name="Callahan">{{cite journal |last1=Callahan |last2=Smith |first2=K.E. |last3=Cleaves |first3=H.J. |last4=Ruzica |first4=J. |last5=Stern |first5=J.C. |last6=Glavin |first6=D.P. |last7=House |first7=C.H. |last8=Dworkin |first8=J.P. |date=11 August 2011 |title=Carbonaceous meteorites contain a wide range of extraterrestrial nucleobases |publisher=[[PNAS]] |doi=10.1073/pnas.1106493108 |pmid=21836052 |pmc=3161613 |volume=108 |issue=34 |journal=[[Proceedings of the National Academy of Sciences of the United States of America]] |pages=13995–8 |bibcode=2011PNAS..10813995C |doi-access=free }}</ref><ref name="Steigerwald">{{cite web |last=Steigerwald |first=John |title=NASA Researchers: DNA Building Blocks Can Be Made in Space |url=http://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |publisher=[[NASA]] |date=8 August 2011 |access-date=2011-08-10 |archive-date=2015-06-23 |archive-url=https://web.archive.org/web/20150623004556/http://www.nasa.gov/topics/solarsystem/features/dna-meteorites.html |url-status=dead }}</ref><ref name="DNA">{{cite web |title=DNA Building Blocks Can Be Made in Space, NASA Evidence Suggests |url=https://www.sciencedaily.com/releases/2011/08/110808220659.htm |date=9 August 2011 |website=[[ScienceDaily]] |access-date=2011-08-09 }}</ref>