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Adding UV light helps form "Missing G" of RNA building blocks
Georgia Institute of Technology | 14 June 2010
NASA Astrobiology Magazine | 19 June 2010
Guanine, Adenine, and Hypoxanthine Production in UV-Irradiated Formamide Solutions:
For scientists attempting to understand how the building blocks of RNA originated on Earth, guanine -- the G in the four-letter code of life -- has proven to be a particular challenge. While the other three bases of RNA -- adenine (A), cytosine (C) and uracil (U) -- could be created by heating a simple precursor compound in the presence of certain naturally occurring catalysts, guanine had not been observed as a product of the same reactions.
By adding ultraviolet light to a model prebiotic reaction, researchers from the Georgia Institute of Technology and the University of Roma, “La Sapienza”, have discovered a route by which the missing guanine could have been formed. They also found that the RNA bases may have been easier to form than previously thought -- suggesting that starting life on Earth might not have been so difficult after all.
The findings are reported June 14, 2010 in the journal ChemBioChem. This collaborative work is supported by the National Science Foundation (NSF), the National Aeronautics and Space Administration, and the European Space Agency. The NSF funding is provided through the Center for Chemical Evolution at Georgia Tech.
Understanding how life emerged is one of the greatest scientific challenges. There is considerable evidence that the evolution of life passed through an early stage in which RNA played a more central role, before DNA and protein enzymes appeared.
The study demonstrated that guanine, adenine and hypoxanthine can be produced at lower temperatures than previously reported, even in the absence of minerals, as long as photons are added.
Relaxation of the Requirements for Prebiotic Purine Nucleobase Formation
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<<Some think that, at the origin of life on Earth, the first adenine was formed by the polymerization of five hydrogen cyanide (HCN) molecules.>>
<<Guanine etymologically comes via the Quichua word "huanu" for dung from the Spanish loan word "guano". Guanine is "A white amorphous substance obtained abundantly from guano, forming a constituent of the excrement of birds". The first isolation of guanine was reported in 1844 from the excreta of sea birds, known as guano, which was used as a source of fertilizer. About fifty years later, Fischer determined the structure and also showed that uric acid can be converted to guanine.
Spiders and scorpions convert ammonia, as a product of protein metabolism in the cells, to guanine as it can be excreted with minimal water loss. Guanine is found in integumentary system of many fish such as sturgeon. It is also present in the reflective deposits of the eyes of deep-sea fish and some reptiles such as Crocodiles.
In 1656 in Paris, François Jaquin (a rosary maker) extracted from scales of some fishes the so-called pearl essence, crystalline guanine. In the cosmetics industry, crystalline guanine is used as an additive to various products (e.g., shampoos), where it provides a pearly 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 is currently in favor in New York, reportedly because the guanine in the droppings produces a clear, "bright" skin tone that some people find desirable to attain. Guanine crystals are rhombic platelets composed of multiple transparent layers, but they have a high 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), and aluminium and bronze particles.>>