Pentose nucleic acid

In successful sugar syntheses (see Sect. 4.4), for example, in the chemistry of gly-colaldehyde phosphate, the problem arose as to why only pentose nucleic acids are... 

Uridine 5 -Diphosphate. Uridine 5. (trihydrogen diphosphate) UDP uridine 5 -pyrophosphate uridine-5-pyrophosphoric acid. C9HI4N20,jPj mol wt 404.18. C 26.75%, H 3.49%, N 6.93%, O 47.50%, P 15.33%. Can be isolated from calf s fiver, thymus, and yeast. The commer -cial product is derived from yeast. Pentose nucleic acids (isolated from yeast) are digested with rattlesnake venom (freed of 5 -monoesterase) and the nucleotides are separated by chromatography Cohn, Volkin, Arch, Biochem. Biophys. 35, 465 (1952) J. Biol Chem. 203, 319 (19S3). For alternate procedures see the refs under Uridine Diphosphate Glucose. Syntheses Chambers, J. Am. Chem. Soc. 81, 3032 (1959) Moffatt, Khorana, ibid. 83, 649 (1961). 

Pentose nucleic acids are degraded by various enzyme systems to yield mononucleotides, and the resulting purine compounds are converted stepwise to uric acid. For example, the purine mononucleotide, adenyhc acid (adenosine-5 -phosphate), can be hydrolytically deaminated by 5-adenylic acid deaminase to yield inosinic acid, or it can be directly... 

PNA pentose nucleic acid, desoxyribose nu cleic acid... 

Cells require a constant supply of N/ X)PH for reductive reactions vital to biosynthetic purposes. Much of this requirement is met by a glucose-based metabolic sequence variously called the pentose phosphate pathway, the hexose monophosphate shunt, or the phosphogluconate pathway. In addition to providing N/VDPH for biosynthetic processes, this pathway produces ribos 5-phosphate, which is essential for nucleic acid synthesis. Several metabolites of the pentose phosphate pathway can also be shuttled into glycolysis. 

This enzyme interconverts ribulose-5-P and ribose-5-P via an enediol intermediate (Figure 23.30). The reaction (and mechanism) is quite similar to the phosphoglucoisomerase reaction of glycolysis, which interconverts glucose-6-P and fructose-6-P. The ribose-5-P produced in this reaction is utilized in the biosynthesis of coenzymes (including N/ DH, N/ DPH, F/ D, and Big), nucleotides, and nucleic acids (DNA and RNA). The net reaction for the first four steps of the pentose phosphate pathway is... 

D-Ribose Nucleic acids. Structural elements of nucleic acids and coenzymes, eg, ATP, NAD, NADP, flavo-proteins. Ribose phosphates are intermediates in pentose phosphate pathway. ... 

The pentose phosphate pathway is an alternative route for the metabolism of glucose. It does not generate ATP but has two major functions (1) The formation of NADPH for synthesis of fatty acids and steroids and (2) the synthesis of ribose for nucleotide and nucleic acid formation. Glucose, fructose, and galactose are the main hexoses absorbed from the gastrointestinal tract, derived principally from dietary starch, sucrose, and lactose, respectively. Fructose and galactose are converted to glucose, mainly in the liver. 

Deoxv-n-ery thro -pentose ( 2-deoxy-D-ribose ) H H H HOHsC—C—C—C—CHO HO HO H nucleic acids... 

Plant metabolism can be separated into primary pathways that are found in all cells and deal with manipulating a uniform group of basic compounds, and secondary pathways that occur in specialized cells and produce a wide variety of unique compounds. The primary pathways deal with the metabolism of carbohydrates, lipids, proteins, and nucleic acids and act through the many-step reactions of glycolysis, the tricarboxylic acid cycle, the pentose phosphate shunt, and lipid, protein, and nucleic acid biosynthesis. In contrast, the secondary metabolites (e.g., terpenes, alkaloids, phenylpropanoids, lignin, flavonoids, coumarins, and related compounds) are produced by the shikimic, malonic, and mevalonic acid pathways, and the methylerythritol phosphate pathway (Fig. 3.1). This chapter concentrates on the synthesis and metabolism of phenolic compounds and on how the activities of these pathways and the compounds produced affect product quality. 

Since only less than 10% of G-6-P is channeled into the pentose phosphate cycle (under physiological conditions this percentage varies depending on the different tissues), the question must be discussed, what is the importance of this shunt. With regard to the resulting compounds Eqs. [(3), (5), (6), (7)] one mole NADPH2 appears twice. Furthermore, pentose phosphates are furnished for biosynthesis of nucleotides, nucleic acids, and fatty acids (D5, D6, DIO, H13, M5). 

Those nucleosides found in the nucleic acids DNA and RNA involve the joining of ribose of deoxyribose to a purine or a pyrimidine base. One such nucleoside is adenosine, in which a nitrogen of adenine is linked to carbon 1 of the pentose, ribose. In this form it is a component of RNA but as a phosphory-lated derivative of adenosine (e.g. ATP), which is a high energy compound, it fulfils an important role in metabolism. The dinucleotides NAD and NADP are two cofactors necessary for many enzymic transformations and these also contain /V-glycosides of ribose phosphate. Other important nucleosides are found... 

The nucleotides of RNA and DNA consist of three components a carbohydrate, a phosphate group and an organic nitrogenous base. There are two types of carbohydrate molecule in nucleic acids, both of which are D-pentoses, i.e. contain five carbon atoms. The carbohydrate in RNA is ribose, while DNA contains deoxyribose, which has a hydrogen atom instead of a hydroxyl group attached to the carbon in the 2 position (Figure 13.1). 

Nucleic acids (DNA and RNA) are assembled liom nucleotides, which consist of three components a nitrogenous base, a five-carbon sugar (pentose), and phosphate. 

The basic structural unit of carbohydrates is the monosaccharide. Molecules in this class contain just one sugar moiety ahexose, pentose, or whatever. Monosaccharides are the building blocks of more complex carbohydrates in mnch the same sense that amino acids are the building blocks for proteins and nncleotides are the building blocks for nucleic acids. 

This pathway is variously known as the pentose phosphate, hexose monophosphate or phosphogluconate pathway, cycle or shunt. Although the pentose phosphate pathway achieves oxidation of glucose, this is not its function, as indicated by the distribution of the pathway in different tissues. Only one of the carbons is released as CO2, the key products are NADPH and ribose 5-phosphate, both of which are important for nucleotide phosphate formation and hence for synthesis of nucleic acids (Chapter 20). The... 

Nucleic acids are broken down into their components by nucleases from the pancreas and small intestine (ribonucleases and deoxyribonucleases). Further breakdown yields the nucleobases (purine and pyrimidine derivatives), pentoses (ribose and deoxyribose). 

FIGURE 7-1 Representative monosaccharides, (a) Two trioses, an aldose and a ketose. The carbonyl group in each is shaded, (b) Two common hexoses. (c) The pentose components of nucleic acids. D-Ribose is a component of ribonucleic acid (RNA), and 2-deoxy-o-ribose is a component of deoxyribonucleic acid (DNA). 

Nucleotides and Nucleic Acids Have Characteristic Bases and Pentoses... 

Nucleic acids have two kinds of pentoses. The recurring deoxyribonucleotide units of DNA contain 2 -deoxy-D-ribose, and the ribonucleotide units of RNA contain D-ribose. In nucleotides, both types of pentoses are in their j3-furanose (closed five-membered ring) form. As Figure 8-3 shows, the pentose ring is not planar but occurs in one of a variety of conformations generally described as puckered. ... 

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