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Synthesis of Pyrimidine Ribonucleotides

Pyrimidine salvage is effective in the treatment of orotic aciduria, a disorder of pyrimidine nucleotide synthesis.

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Nyhan, W. L. 2014. Nucleotide Synthesis via Salvage Pathway. eLS. .

We report the synthesis and evaluation of several unnatural ribotriphosphates bearing linkers that allow the chemoselective attachment of different functionalities. One unnatural base pair is used to dual label a 243-nt fragment of a 16S RNA with Cy3 and Cy5, which are then used to characterize conformational changes in the presence of ribosomal proteins.

The Hard salvage pathway for synthesis of purine il to reach the home share.

Boursaux‐Eude C, Margarita D, Gilles AM, Barzu O and Saint Girons I (1997) Borrelia burgdorferi uridine kinase: an enzyme of the pyrimidine salvage pathway for endogenous use of nucleotides. FEMS Microbiology Letters 151: 257–261.

Nyhan, W. L. 2005. Nucleotide Synthesis via Salvage Pathway. eLS. .

Pyrimidine salvage is catalysed by thymidine kinase.

Synthesis of purine ribonucleotides
IMP is synthesized from ribose 5-phosphate. There are 11 reactions in the formation of IMP. IMP is converted to GMP and AMP with the help of ATP and GTP respectively. Nucleoside monophosphates are converted to nucleoside diphosphates by base specific monophosphate kinases. Purine nucleotide synthesis is regulated by feedback inhibitor – AMP, GMP and IMP. An important regulatory factor is the availability of PRPP. Salvage pathway for purines is observed in RBC and the brain. Free purines are salvaged by APRTase and HGPRTase enzymes

Synthesis of pyrimidine ribonucleotides
Pyrimidine ring is synthesized as free pyrimidine and then it is incorporated into the nucleotide. 6 reactions are involved in the synthesis of UMP. UDP and UTP are synthesized from UMP with the help of ATP. CTP is formed by adding an amino group from glutamine. Pyrimidine can also be salvaged using PRPP. In orotic aciduria, excretion of large amount of orotic acid is observed. It results from the deficiency of either orotate phospho ribosyl transferase or OMP decarboxylase.

Substrates for salvage pathways can come from intracellular nucleic acid degradation (see DNA Degradation In Vivo). For most cells, however, salvage precursors are derived from the extracellular environment. An extreme example is protozoan parasites, which derive all their nucleic acid precursors from salvage substrates in the blood of infected organisms. In fact, these parasites have evolved to the extent that they completely lack de novo pathways and are totally dependent on salvage (1, 2); development of specific salvage inhibitors now constitutes one of the most active research areas of biochemical parasitology.


We can both synthesize them de novo andsalvage and reuse those we already have.

Because nearly all cells possess de novo nucleotide synthetic capabilities, the salvage enzymes are usually not required for cell viability. In addition, a large number of nucleobase and nucleoside antimetabolites are available, most of them inhibitors of specific enzymes (see Nucleotides, Nucleosides, And Nucleobases). These factors create favorable conditions for the use of salvage enzymes as selectable genetic markers, ie, genetic characteristics that promote the selective survival or growth of desired cell types. For example, the mammalian enzyme encoding HGPRT is widely used as a selectable marker in genetic analysis. 6-Thioguanine is metabolized by HGPRT to give the thiol analogue of inosinic acid, which is toxic. Cells lacking HGPRT can be selected for because they grow in 6-thioguanine-containing medium, while other cells are killed. Hence, one can estimate mutation rates by culturing wild-type cells in the presence of thioguanine and enumerating the cells that grow. Another advantage of this gene for genetic analysis is that it is carried on the X-chromosome. Thus, in male-derived cell lines, only one mutation, rather than two independent events is required to give the resistant phenotype.

Simmonds HA and van Gennip AH (2003) Purine and pyrimidine disorders. In: Blau N, Duran M, Blaskovics M and Gibson KM (eds) Physician's Guide to the Laboratory Diagnosis of Metabolic Diseases, pp. 445–465. Berlin: Springer.

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  • Protein synthesis protein degradation.

    Iltzsch MH (1993) Pyrimidine salvage pathways in Toxoplasma gondii. Journal of Eukaryotic Microbiology 40: 24–28.

  • Nucleotide Synthesis via Salvage Pathway

    Murray AW (1971) The biological significance of purine salvage. Annual Review of Biochemistry 40: 811–826.

  • De novo and salvage pathway of purines - SlideShare

    Pyrimidine salvage is effective in the treatment of orotic aciduria, a disorder of pyrimidine nucleotide synthesis.

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de novo and salvage pathway of purines

On the other hand, one can select for the presence of active salvage enzymes. The best example is the use of "HAT medium" in somatic cell genetic analysis and in preparing monoclonal antibodies. These techniques involve fusing cells of different origins and culturing in HAT medium to select for those cells that have undergone fusion. HAT is an acronym for the medium’s constituents,— hypoxanthine, aminopterin, and thymidine. Aminopterin inhibits dihydrofolate reductase, blocking the synthesis of tetrahydrofolate needed for de novo synthesis of purine nucleotides and thymidine nucleotides. Thus, cells can grow in HAT medium only if they express active thymidine kinase and HGPRT, for salvage synthesis of thymidine and purine nucleotides, respectively. In monoclonal antibody production, one of the cell lines to be fused lacks thymidine kinase, and the other lacks HGPRT. Thus, only cells resulting from a fusion event have functional copies of both enzymes and can grow.

Purine & Pyrimidine Synthesis (de-novo) | …

Murray AW, Elliott DC and Atkinson MR (1970) Nucleotide biosynthesis from preformed purines in mammalian cells: regulatory mechanisms and biological significance. Progress in Nucleic Acid Research and Molecular Biology 10: 87–119.

Salvage pathway of purines - YouTube

A final example relates to the use of a selectable marker to force expression of a nonselected marker. For cloning into expression systems in mammalian cells, one often incorporates into the cloning vector the Escherichia coli xpt gene, which encodes a distinctive phosphoribosyltransferase that acts on xanthine and guanine. During and after transformation of cells with the recombinant DNA, the cells are cultured in the presence of mycophenolic acid, which blocks de novo guanine nucleotide synthesis by inhibiting IMP dehydrogenase, the enzyme that converts IMP to XMP (which would then be converted to GMP). Thus, the only cells that can grow are those that have taken up and expressed the xpt gene, which bypasses this metabolic block. Being carried on the same vector, the gene of interest is also cloned and/or expressed, even though its expression was not directly selected for.

Enzymic capacities of purine de Novo and salvage …

Therefore, in order to generate a therapeutically effective nucleotide intracellularly, its precursor must be administered extracellularly as a nucleobase or nucleoside analogue. Effective use of such drugs demands extensive understanding of salvage pathways in the target cell, subcellular distribution of the enzymes involved, degradative enzymes that might compete with the pathway leading to the desired nucleotide analogue, levels of the target enzyme, and cell-cycle regulation of all the enzymes involved (8).

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