РНК құрамындағы урацил туралы мәліметтер

Chemical compound of RNA

Uracil ('/j//ʊər//ə//s//ɪ//l/) (symbol U or Ura) is one of the four nucleobases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced by thymine (T). Uracil is a demethylated form of thymine. Uracil is a common and naturally occurring pyrimidine derivative. The name "uracil" was coined in 1885 by the German chemist Robert Behrend, who was attempting to synthesize derivatives of uric acid. Originally discovered in 1900 by Alberto Ascoli, it was isolated by hydrolysis of yeast nuclein; it was also found in bovine thymus and spleen, herring sperm, and wheat germ. In DNA, the evolutionary substitution of thymine for uracil may have increased DNA stability and improved the efficiency of DNA replication (discussed below). Uracil pairs with adenine through hydrogen bonding. When base pairing with adenine, uracil acts as both a hydrogen bond acceptor and a hydrogen bond donor. In RNA, uracil binds with a ribose sugar to form the ribonucleoside uridine. When a phosphate attaches to uridine, uridine 5′ monophosphate is produced. Uracil undergoes amide imidic acid tautomeric shifts because any nuclear instability the molecule may have from the lack of formal aromaticity is compensated by the cyclic amidic stability. The negative charge is placed on the oxygen anion and produces a pKa of less than or equal to 12. The basic pKa = −3.4, while the acidic pKa = 9.389. In the gas phase, uracil has four sites that are more acidic than water.

Organisms synthesize uracil, in the form of uridine monophosphate (UMP), by decarboxylating orotidine 5' monophosphate (orotidylic acid). In humans this decarboxylation is achieved by the enzyme UMP synthase. In contrast to the purine nucleotides, the pyrimidine ring (orotidylic acid) that leads uracil is synthesized first and then linked to ribose phosphate, forming UMP.

There are many laboratory synthesis of uracil available. The first reaction is the simplest of the syntheses, by adding water to cytosine to produce uracil and ammonia:

In 2009, NASA scientists reported having produced uracil from pyrimidine and water ice by exposing it to ultraviolet light under space like conditions. This suggests a possible natural original source for uracil. In 2014, NASA scientists reported that additional complex DNA and RNA organic compounds of life, including uracil, cytosine and thymine, have been formed in the laboratory under outer space conditions, starting with ice, pyrimidine, ammonia, and methanol, which are compounds found in astrophysical environments. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), a carbon rich chemical found in the Universe, may have been formed in red giants or in interstellar dust and gas clouds. Based on 12C/13C isotopic ratios of organic compounds found in the Murchison meteorite, it is believed that uracil, xanthine, and related molecules can also be formed extraterrestrially. Data from the Cassini mission, orbiting in the Saturn system, suggests that uracil is present in the surface of the moon Titan. In 2023, uracil was observed in a sample from 162173 Ryugu, a near Earth asteroid, with no exposure to Earth's biosphere, giving further evidence for synthesis in space.

Uracil readily undergoes regular reactions including oxidation, nitration, and alkylation. While in the presence of phenol (PhOH) and sodium hypochlorite (NaOCl), uracil can be visualized in ultraviolet light. Uracil also has the capability to react with elemental halogens because of the presence of more than one strongly electron donating group.

Uracil's use in the body is to help carry out the synthesis of many enzymes necessary for cell function through bonding with riboses and phosphates. Uracil is important for the detoxification of many carcinogens, for instance those found in tobacco smoke. Uracil is also required to detoxify many drugs such as cannabinoids (THC) and morphine (opioids). It can also slightly increase the risk for cancer in unusual cases in which the body is extremely deficient in folate. Uracil can be used for drug delivery and as a pharmaceutical. When elemental fluorine reacts with uracil, they produce 5 fluorouracil. 5 Fluorouracil is an anticancer drug (antimetabolite) used to masquerade as uracil during the nucleic acid replication process. Uracil has also shown potential as a HIV viral capsid inhibitor. Uracil derivatives have antiviral, anti tubercular and anti leishmanial activity. Uracil can be used to determine microbial contamination of tomatoes. The presence of uracil indicates lactic acid bacteria contamination of the fruit. Uracil derivatives containing a diazine ring are used in pesticides. Uracil derivatives can enhance the activity of antimicrobial polysaccharides such as chitosan. In yeast, uracil concentrations are inversely proportional to uracil permease. Mixtures containing uracil are also commonly used to test reversed phase HPLC columns. As uracil is essentially unretained by the non polar stationary phase, this can be used to determine the dwell time (and subsequently dwell volume, given a known flow rate) of the system.