Ribose nucleotides

The position of attachment of the phosphoric acid to the ribose residue in the ribosenvcleotides. In order to understand the historical development of this aspect of the subject it is necessary first to discuss the chemistry of two ribose nucleotides which, although of great biochemical importance, are not components of ribosenucleic acid. They are both purine nucleotides and both occur free in Nature. 

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The chemical structure of the nucleotides is shown in Figure 7-21. They are purine ribonucleotides with a hydroxyl group on carbon 6 of the purine ring and a phosphate ester group on the 5 -carbon of the ribose. Nucleotides with the ester group at the 2 or 3 position are tasteless. When the ester group is removed by the action of phos-phomonoesterases, the taste activity is lost. It is important to inactivate such enzymes in foods before adding 5 -nucleotide flavor enhancers. 

This was phosphorylated with phosphorus oxychloride in pyridine, and the resulting 5-phospho-isopropylidene-uridine hydrolyzed to give 5-phospho-uridine, a substance whose phosphoryl group is hydrolyzed off at a lower rate than that of any other knowm ribose nucleotide. Hence uridylic acid is not 5-phospho-uridine. 

RNA Ribonucleic acid, a polymer of ribose nucleotides. RNA plays many roles in gene expression. 

Ribonucleic acids (RNAs) Nucieic acids that transmit genetic information and direct protein synthesis contain ribose Nucleotide Biomolecule with a five-carbon sugar bonded to a nucleic acid base and a phosphate group monomer in DNA... 

As already pointed out, quinolinic acid is not directly converted to nicotinic acid. Instead, it reacts with PRPP to yield the 5 -nucleotide. This is followed by decarboxylation of the ribose nucleotide of quinolinic acid. The same protein, quinolinate transphosphory-lase, may catalyze both the formation of the glycosidic bond and the decarboxylation. 

In some bacteria, vitamin B12 can be replaced in the culture medium by deoxyribosides, thus suggesting that vitamin Bi 2 plays a role in the conversion of ribose to deoxyribose. Diphosphate ribose nucleotide usually serves as the substrate for the enzyme. The 2-hydroxyl group of the ribose nucleotide is directly replaced by a hydrogen. The exact mechanism of the hydrogen transfer is not known, but it is believed to occur in the form of a hybrid ion, which is derived from a reducing agent. 

RNA (Ribonucleic Acid) Single-stranded polymer consisting of ribose nucleotides formed by transcription of DNA or viruses from another RNA strand. 

In addition to the sugar component, at the 5 -position of the ribose, nucleotides contain a mono-, di-, or triphosphate group. 

Synthesis of Polyribonucleotides. The synthesis of large polymers of ribose nucleotides is catalyzed by an enzyme named polynucleotide phosphorylase. This enzyme was first found in extracts of Azotobacter vinelandii, and similar preparations have been obtained in other bacteria. This type of enzyme has not yet been identified in animal tissues. 

Fig. 2. Stereochemical comparison of 3 -FMP (syn) (solid line) and an H-bonding hybrid of 3 -CMP and 3 -UMP (anti) (dashed line). The torsion angles about the glycosyl bonds differ by 180° in the two nucleotides. All other torsion angles are identical and are like those in ribose nucleotides of helical RNA.

Almost all coenzymes contain phosphoric acid as an essential component, often in a type of bond called nucleoside phosphate, or better nucleotide. Nucleotides consist of a base, a monosaccharide (nearly always ribose), and phosphoric acid. The base and sugar are linked through an N-glycoside bond (cf. Chapt. VII-1) the phosphoric acid is esterified with one hydroxyl group of the ribose. Nucleotides... 

Nucleic Acid Polymer of deoxyribose nucleotides Polymer of ribose nucleotides... 

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