Ribose phosphate synthesis

The atoms of the purine ring are contributed by a number of compounds, including amino acids (aspartic acid, glycine, and glutamine), CO2, and N10-formyltetrahydrofolate (Figure 22.5). The purine ring is constructed by a series of reactions that add the donated carbons and nitrogens to a preformed ribose 5-phosphate. (See p. 145 for a discussion of ribose 5-phosphate synthesis by the HMP pathway.)... 

The enzymes of ribose phosphate synthesis are listed in Table 6-II. 

RNA is synthesized in the latter case, and since the DNA synthesis is stimulated about fourfold, there appears to be a shunt of ribose phosphate synthesis to desoxyribose phosphate synthesis in virus infection. Since nucleic acid P accounts for about 80% of the phosphorus of the cell, it is evident that this redistribution of pentose P involves a major redistribution of phosphorus metabolism. 

As Fig. 6.11 shows, the normal ribose phosphate chain of native RNA is replaced by the simpler backbone of polyamide polymers. The laboratory synthesis of these new polymers has been carried out. 

Phosphoribosylpyrophosphate (PRPP) synthetase is one of the very few enzymes which transfer a pyrophosphoryl group from ATP in one step. When the synthesis is carried out in lsO-enriched water, lsO is incorporated into the PRPP, but not into AMP.91 The lsO in the PRPP arises from a pre-exchange between the H2180 and the ribose phosphate, and hence the results confirm that fission of the /5-P—O bond takes place. PRPP and ATP are starting materials in the biosynthesis of histidine, and Ai-(5 -phospho-D-ribosyl)adenosine triphosphate (29) is an intermediate. The... 

The final control mechanism is the inhibition of PRPP synthesis by the allosteric regulation of ribose phosphate pyrophosphokinase. This enzyme is inhibited... 

PRPP is an "activated pentose" that participates in the synthesis of purines and pyrimidines, and in the salvage of purine bases (see p. 294). Synthesis of PRPP from ATP and ribose 5-phosphate is catalyzed by PRPP synthetase (ribose phosphate pyrophosphokinase, Figure 22.6). This enzyme is activated by inorganic phosphate (Pi) and inhibited by purine nucleotides (end-product inhibition). [Note The sugar moiety of PRPP is ribose, and therefore ribonucleotides are the end products of de novo purine synthesis. When deoxy-ribonucleotides are required for DNA synthesis, the ribose sugar moiety is reduced (see p. 295).]... 

Purine nucleotides can be synthesized in three ways By de novo synthesis, by reconstruction from purine bases through the addition of a ribose phosphate moiety, or by phosphory-... 

The biosynthetic pathway to UMP starts from carbamoyl phosphate and results in the synthesis of the pyrimidine orotate, to which ribose phosphate is subsequently attached. CTP is subsequently formed from UTP. Deoxyribonucleotides are formed by reduction of ribonucleotides (diphosphates in most cells). Thy-midylate is formed from dUMP. 

The backbone of a nucleic acid is a polymer of ribofuranoside rings (five-membered rings of the sugar ribose) linked by phosphate ester groups. Each ribose unit carries a heterocyclic base that provides part of the information needed to specify a particular amino acid in protein synthesis. Figure 23-21 shows the ribose-phosphate backbone of RNA. 

The pyrimidine ring is assembled first and then linked to ribose phosphate to form a pyrimidine nucleotide. PRPP is the donor of the ribose phosphate moiety. The synthesis of the pyrimidine ring starts with the formation of carbamoylaspartate from carbamoyl phosphate and aspartate, a reaction catalyzed by aspartate transcarbamoylase. Dehydration, cyclization, and oxidation yield orotate, which reacts with PRPP to give orotidylate. Decarboxylation of this pyrimidine nucleotide yields UMP. CTP is then formed by the amination of UTP. 

Activated ribose phosphate. Write a balanced equation for the synthesis of PRPP from glucose through the oxidative branch of the pentose phosphate pathway. 

The branch starting with anthranilate leads to the synthesis of trypto phan (Figure 24.15). Chorismate acquires an amino group derived from the hydrolysis of the side chain of glutamine and releases pyruvate to forin anthranilate. Then anthranilate condenses with 5-phosphoribosyl-l-pyrophosphate (PRPP), an activated form of ribose phosphate. PRPP is also... 

In de novo synthesis of pyrimidines, the ring is synthesized first and then it is attached to a ribose phosphate to form a pyrimidine nucleotide (Figure 25.2), Pyrimidine rings are assembled from bicarbonate, aspartate, and ammonia. Although an ammonia molecule already present in solutioii can... 

The purine ring is assembled from a variety of precursors glutamine, glycine, aspartate, N formyltetrahydrofolate, and (XT. The committed step in the de novo synthesis of purine nucleotides is the formation of 5-phosphoribosyIamine from PRPP and glutamine. The purine ring is assembled on ribose phosphate, in contrast with the de novo synthesis of pyrimidine nucleotides. The addition of glycine,... 

The answer is c, (Murray, pp 375-801. Scriver, pp 2513-2570. Sack, pp 121-138. Wilson, pp 287-320.) 5 -phosphoribosyl-l-pyrophosphate (PRPP) donates the ribose phosphate unit of nucleotides and is absolutely required for the beginning of the synthesis of purines. In fact, the enzymes regulating the synthesis of PRPP and the subsequent synthesis of phospho-ribosylamine from PRPP are all end product-inhibited by inosine... 

In a large number of publications the use of 3-hydroxy-1,2,3-benzotriazin-4(3//)-one (4) as a condensation agent in peptide synthesis is described. Finally, the imidazo[4,5-r/]-l,2,3-triazines, e.g. 5, represent the 2-azapurine system. Therefore, in many papers, the biological activity of 2-azaadenine (6) or 2-azahypoxanthine (7), its ribose derivatives and its ribose phosphates were discussed. 

Azathioprine (Imuran) Converted to 6-mercaptopurine ribose phosphate which inhibits purine synthesis. Because DNA RNA synthesis requires proteins, all proliferating cells are inhibited (B-cells, T-cells, nonimmune cells). Prevention of organ transplant rejection. Gl distress, bone marrow depression, infections, mild leukopenia and thrombocytopenia. 

The growing ring system of purines is attached to ribose phosphate during the synthesis process. 

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