Ribose nucleic acid

Nature is also selective in the geometry involved in nucleic acid synthesis. This specificity involves both the base order and the particular sugar employed. For DNA the employed sugar is (3-2-deoxy-D-ribose, deoxyribose (below left). Deoxyribose has three chiral centers but only one of them is employed in the synthesis of nucleic acids. Ribose, the sugar employed in the synthesis of RNA, has four geometric sites (below right). 

First, given the wide range of prebiotic nucleic acids, ribose-based polymers may be the most eminently suited for catalysis. Eschenmoser has pointed out, for example, that nucleic acids constructed from hexose nucleotides form inflexible ribbon structures,61 poorly suited for convoluting into the complex shapes that are required for catalysis (e.g., the backbone of the projected tertiary structure of the Tetrahymena self-splicing intron folds back on itself a number of times).62 Conversely, backbones composed of acyclic nucleotides may be too flexible to adopt stable secondary structures (since a great deal of entropy would necessarily be lost on freezing into a given conformer). Ribose, on the other hand, has a limited flexibility because of its pseudorotation cycle, and RNA can adopt a variety of helical conformations. 

The four principal bases of the nucleic acids are uracil and cytosine, which are derivatives of pyrimidine, and adenine and guanine, which are derived from the purine heterocycle (Fig. 15.1). In the nucleic acids, ribose (in ribonucleic acid,... 

As there are no reports of adverse effects from consumption of excess thiamine from food and supplements (supplements of 50 mg/day are widely available without prescription), and the data are inadequate for a quantitative risk assessment, no UL has been defined for thiamine. However, as stimulators of transketolase enzyme synthesis such as thiamine support a high rate of nucleic acid ribose synthesis necessary for tumor cell survival, chemotherapy resistance, and proliferation, some concern has been expressed that thiamine supplementation of common food products may contribute to increased cancer rates in the Western world. There is, however, littie evidence to support this assumption. Rarely, individuals given high-dose intravenous thiamine in treatment of beriberi have developed anaphylaxis, the frequency being about 1 100,000. 

Miescher was the first to investigate the biochemical composition of cell nuclei. He prepared nuclei derived from pus and discovered a specific nuclear component that he named nuclein. About 20 years later, Holt-man discovered that the compound isolated by Miescher was acidic, and that phosphorus was responsible for the acidic properties therefore, nuclein was renamed nucleic acid. Later it was found that there were two types of nucleic acids—ribose and deox-... 

Thymo-nucleic acid, desoxyribose nucleic acid. Yeast-nucleic acid, ribose nucleic acid. 

Pentose sugars are required for the synthesis of nucleic acids. Ribose 5-phosphate is utilized in the synthesis of purine and pyrimidine deoxyribo- and ribo-nucleotides. Since neonatal and fetal thymuses are highly active in nucleic acid synthesis, these tissues have an active pentose phosphate pathway to furnish ribose 5-phosphate. Ribose moieties also feature in the structure of major coenzymes such as NAD(P), coenzyme A and FAD (Figure 5.3). The degradation of nucleic acids and nucleotides... 

C4H4N2O2. Colourless crystalline powder, turning brown at 280 C and melting at 338 C (decomp.). Uracil is a constituent of ribose nucleic acid. Used as a diuretic and derivatives have pharmaceutical importance. 5-Fluorouracil is used in cancer treatment. 

Even if It could be shown that RNA preceded both DNA and proteins in the march toward living things that doesn t automatically make RNA the first self replicating molecule Another possibility is that a self replicating polynucleotide based on some carbo hydrate other than o ribose was a precursor to RNA Over many generations natural selection could have led to the replacement of the other carbohydrate by D ribose giving RNA Recent research on unnatural polynucleotides by Professor Albert Eschenmoser of the Swiss Federal Institute of Technology (Zurich) has shown for example that nucleic acids based on L threose possess many of the properties of RNA and DNA... 

Section 28 7 Nucleic acids are polynucleotides present m cells The carbohydrate component is D nbose m ribonucleic acid (RNA) and 2 deoxy d ribose m deoxyribonucleic acid (DNA)... 

Any one nucleotide, the basic building block of a nucleic acid, is derived from a molecule of phosphoric acid, a molecule of a sugar (either deoxyribose or ribose), and a molecule of one of five nitrogen compounds (bases) cytosine (C), thymine (T), adenine (A), guanine (G), uracil (U). 

Nucleic Acids. Phosphoms is an essential component of nucleic acids, polymers consisting of chains of nucleosides, a sugar plus a nitrogenous base, and joined by phosphate groups (43,44). In ribonucleic acid (RNA), the sugar is D-ribose in deoxyribonucleic acids (DNA), the sugar is 2-deoxy-D-ribose. 

The sugars are typically ribose (ribonucleic acids, RNA), or 2-deoxyribose (deoxyribonucleic acids, DNA). There are five common bases in nucleic acids adenine (A) thymine (T) uracil (U) cytosine (C) and guanine (G). DNA polymers incorporate the four bases. A, T, C, and G, and RNA, the set A, U, C, and G. 

Ribonucleic acid (RNA) A nucleic acid that contains the sugar ribose. 

FIGURE 1.9 (a) Amino acids build proteins by connecting the n-carboxyl C atom of one amino acid to the n-amino N atom of the next amino acid in line, (b) Polysaccharides are built by combining the C-1 of one sugar to the C-4 O of the next sugar in the polymer, (c) Nucleic acids are polymers of nucleotides linked by bonds between the 3 -OH of the ribose ring of one nucleotide to the 5 -P04 of its neighboring nucleotide. All three of these polymerization processes involve bond formations accompanied by the elimination of water (dehydration synthesis reactions). 

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... 

As is well-known, nucleic acids consist of a polymeric chain of monotonously reiterating molecules of phosphoric acid and a sugar. In ribonucleic acid, the sugar component is represented by n-ribose, in deoxyribonucleic acid by D-2-deoxyribose. To this chain pyrimidine and purine derivatives are bound at the sugar moieties, these derivatives being conventionally, even if inaccurately, termed as pyrimidine and purine bases. The bases in question are uracil (in ribonucleic acids) or thymine (in deoxyribonucleic acids), cytosine, adenine, guanine, in some cases 5-methylcytosine and 5-hydroxymethylcyto-sine. In addition to these, a number of the so-called odd bases occurring in small amounts in some ribonucleic acid fractions have been isolated. 

The nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are biological polymers that act as chemical carriers of an organism s genetic information. Enzyme-catalyzed hydrolysis of nucleic acids yields nucleotides, the monomer units from which RNA and DNA are constructed. Further enzyme-catalyzed hydrolysis of the nucleotides yields nucleosides plus phosphate. Nucleosides, in turn, consist of a purine or pyrimidine base linked to Cl of an aldopentose sugar—ribose in RNA and 2-deoxyribose in DNA. The nucleotides are joined by phosphate links between the 5 phosphate of one nucleotide and the 3 hydroxyl on the sugar of another nucleotide. 

The DNA monomers are each completed by a phosphate group, —O—P032, covalently bonded to carbon atom 5 of the ribose unit to give a compound called a nucleotide (28). Because there are four possible nucleoside monomers (one for each base), there are four possible nucleotides in each type of nucleic acid. 

The Chemistry of Ribose and Deoxyribose, W. G. Overend and M. Stacey, Chapter 2 in The Nucleic Acids, Vol I. Chemistry and Biology, Edited by E. Chargaff and J. N. Davidson, Academic Press, (1955) 9- 80. 

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 monosaccharides include glucose, the blood sugar and ribose, an important constiment of nucleotides and nucleic acids. 

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. 

Ribulose 5-phosphate is the substrate for two enzymes. Ribulose 5-phosphate 3-epimerase alters the configuration about carbon 3, forming another ketopentose, xylulose 5-phosphate. Ribose 5-phosphate ketoisom-erase converts ribulose 5-phosphate to the corresponding aldopentose, ribose 5-phosphate, which is the precursor of the ribose required for nucleotide and nucleic acid synthesis. Transketolase transfers the two-carbon... 

The most important product of the hexose monophosphate pathway is reduced nicotinamide-adenine dinucleotide phosphate (NADPH). Another important function of this pathway is to provide ribose for nucleic acid synthesis. In the red blood cell, NADPH is a major reducing agent and serves as a cofactor in the reduction of oxidized glutathione, thereby protecting the cell against oxidative attack. In the syndromes associated with dysfunction of the hexose monophosphate pathway and glutathione metabolism and synthesis, oxidative denaturation of hemoglobin is the major contributor to the hemolytic process. 

The photochemistry of the polynucleotides has been elucidated primarily by studies of the photochemical behavior of the individual pyrimidine and purine bases (the ribose and phosphate groups would not be expected to undergo photochemical reactions in this wavelength range). These studies have shown the pyrimidines (cytosine and thymine) to be roughly ten times more sensitive to UV than the purines (adenine and guanine.) Thus we would expect most of the photochemistry of the nucleic acids to result from the action of light on the pyrimidines. 

Only a few years after the Miller-Urey experiment was published, J. Oro was able to synthesize one of the most important biomolecules, adenine. This purine derivative is not only a component of the nucleic acids, but as ATP, adenosine triphosphate (in combination with ribose and three phosphate residues), it plays a key role in the metabolism of all living creatures. The chemical formula of adenine is C5H5N5, or expressed in another way, (HCN)s. 

About 40 different sugars are formed. Those required for nucleic acid synthesis, ribose and deoxyribose, are obtained in yields of less than 1%. It is completely unclear whether these could have been separated from the others under primeval Earth conditions (Shapiro, 1988). 

The above-mentioned facts require that ribose must have undergone further reactions immediately after its formation under prebiotic conditions. More than 20 years ago R. Shapiro (1984) pointed out the immense problems which would have needed to be solved in prebiotic nucleic acid formation. 

Two points thus argue against the participation of ribose in nucleic acid formation the lability of the molecule and the problems with its synthesis (the concentrations of the starting materials are too high). Other, newer and more effective syntheses seem necessary, whereby prebiotic conditions (although these are not known precisely) strongly limit the possibilities. 

---