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|Section2= |Section3= }} Glycolaldehyde (HOCH2-CH=O) is the smallest possible molecule that contains both an aldehyde group and a hydroxyl group. It is the only possible diose, a 2-carbon monosaccharide, although a diose is not strictly a saccharide. While not a true sugar, it is the simplest sugar-related molecule. Glycolaldehyde is an intermediate in the formose reaction. In the formose reaction, two formaldehyde molecules condense to make glycolaldehyde. Glycolaldehyde then is converted to glyceraldehyde. The presence of this glycolaldehyde in this reaction demonstrates how it might play an important role in the formation of the chemical building blocks of life. Nucleotides, for example, rely on the formose reaction to attain its sugar unit. Nucleotides are essential for life, because they compose the genetic information and coding for life. Glycolaldehyde forms from many precursors, including the amino acid glycine. It can form by action of ketolase on fructose 1,6-bisphosphate in an alternate glycolysis pathway. This compound is transferred by thiamine pyrophosphate during the pentose phosphate shunt. In purine catabolism, xanthine is first converted to urate. This is converted to 5-hydroxyisourate, which decarboxylates to allantoin and allantoic acid. After hydrolyzing one urea, this leaves glycolureate. After hydrolyzing the second urea, glycolaldehyde is left. Two glycolaldehydes condense to form erythrose 4-phosphate, which goes to the pentose phosphate shunt again. Glycolaldehyde is the second most abundant chemical formed when preparing pyrolysis oil (up to 10% by weight). ==Formation on prebiotic Earth== (詳細はmethane, (CH4), ammonia (NH3), water vapor, and other simple gases. These gases were exposed to electrical discharge following the formation of formaldehyde in abundance and glycolaldehyde in lesser amounts. This theory is similar to that of Miller-Urey. After the electrical discharge to early Earth’s atmosphere, formaldehyde and glycolaldehyde then rained down to Earth and were deposited in aquifers that theoretically contained other solvents such as formamide. Formamide has been shown to provide an electrophilic background that is necessary for simple sugars to react further, producing more complex sugars. The aquifers had a high alkaline environment. The Earth’s atmosphere, consisting of CO2, was able to lower the aquifer's pH enabling formation of complex sugars. Some scientists speculate borates in these aquifers were able to permit formation of complex sugars, such as ribose, by forming borate complexes with the final pentose. Glycolaldehyde bound to borate enolized, meaning the carbon oxygen bond gave electrons to the neighboring carbon creating a double bond. The oxygen received hydrogen due to the creation of the double bond. Glycolaldehyde then participated in aldol reactions acting as a nucleophile. This process yielded the first complex sugar on Earth. It should also be noted that laboratory experiments have demonstrated that both amino acids and short dipeptides may have facilitated the formation of complex sugars. For example, L-valyl-L-valine was used as a catalyst to form tetroses from glycolaldehyde. Theoretical calculations have additionally shown the feasibility of dipeptide-catalyzed synthesis of pentoses. This formation showed stereospecific, catalytic synthesis of D-ribose, the only naturally occurring enantiomer of ribose. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Glycolaldehyde」の詳細全文を読む スポンサード リンク
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