Deoxyribose monophosphate nucleotide

In nature, eight common nucleotides exist, four found in DNA and four in RNA. In the standard abbreviations for DNA nucleotides, a lowercase d specifies the presence of deoxyribose. RNA nucleotides lack this designation. Nucleosides have names of one word (e.g., deoxyadenosine, cytidine, and uridine). The ending monophosphate completes the nucleotide names. Table 16.1 lists correct names for all common nucleotides and nucleosides, and Figure 16.9 shows linkages and structures for all eight nucleotides. 

The separation of nucleotides and deoxynucleotides, previously a formidable task involving the fractional crystallization of heavy metal and alkaloid salts 102) has been made much easier by developments in analytical techniques. Ion-exchange methods may be used for the purification, isolation, and identification of both classes of nucleotides from hydrolysis mixtures 103), Countercurrent distribution 104) and starch 106) and cellulose-column 106) as well as paper-strip chromatography 107) have also proved to be useful in separating nucleotides from natural sources. Spectro-photometric procedures based on the characteristic ultraviolet absorption spectra of the purines and pyrimidines have been the most convenient method to locate, estimate, and identify the fractions obtained in the previous separations. Since the nucleotides are acid in nature, they are often named as acids, e.g., adenylic acid, cytidylic acid. The general constitution of the purine nucleotides (and by analogy the pyrimidine nucleotides) is demonstrated by their hydrolysis by acids to a purine and ribose (or 2-deoxyribose) monophosphate and by alkalies to the nucleosides and phosphoric acid. The order of the constituents in a purine nucleotide must, therefore, be ... 

Nucleotides are nucleosides in which a phosphate group bonds to the —OH group on carbon 5 (C5 ) of ribose or deoxyribose. The product is a phosphate ester. Other hydroxyl groups on ribose can form phosphate esters too, but only the 5 -monophosphate nucleotides are found in RNA and DNA. AH the nucleotides in RNA and DNA are shown in Figure 17.4. Table 17.1 summarizes the components in DNA and RNA. 

Excess purine nucleotides or those released from DNA and RNA by nucleases are catabolized first to nucleosides (loss of P.) and then to free purine bases (release of ribose or deoxyribose). Excess nucleoside monophosphates may accumulate when ... 

The names of nucleotides containing both deoxyribose and thymine do not have the prefix deoxy. Inosine-5 -monophosphate (IMP) is an intermediate in purine nucleotide synthesis. The base component of IMP is hypoxanthine. 

The metabolism of pentoses has been studied in detail only recently, chiefly of ribose and to a lesser extent deoxyribose. Horecker and his coworkers (H7) have considered the steps in the hexose monophosphate shunt, and the pentose oxidative or Warburg-Dickens-Lipmann pathway. It appears that this pathway is the source of the pentose moiety of nucleotides, ribonucleic acid, and deoxyribonucleic acid. It is also undoubtedly the source of the small amounts of ribulose in normal urine. 

An alternative nomenclature system for nucleotides emphasizes their acidic properties (a result of the phosphate group). The name of the base unit from the above nomenclature system forms the basis of the name. The ending -osine monophosphate or -ine monophosphate is replaced by -ylic acid. The prefix deoxy- is used as before to distinguish deoxyribose from ribose. 

Nucleotides, nucleoside phosphates phosphoric acid esters of Nucleosides (see). o-Phosphoric add is esterified with a free OH-group of the sugar. If the sugar is D-ribose, the N. is called a ribonucleotide or ribotide. If the sugar is o-2-deoxyribose, the N. is a deoxyribonucleotide, deoxynucleotide or deoxyribo-tide. The phosphate may be present on position 2, 3 or 5 (in deoxyribonucleotides, only the 3 - and 5 -phosphate are possible). 5 -nucleoside phosphates are metabolically very important they may be mono-, di- or triphosphorylated, e.g. guanosine S -monophosphate, cytidine 5 -diphosphate and adenosine 5 -triphosphate. 

Biosynthesis of thymine nucleotides. This is shown in Fig. 2. Since thymine is a constituent of DNA, the corresponding nucleotides contain 2-deoxyribose. Thymidylic acid (TMP) is therefore more correctly dTMP (deoxythymidine 5 -monophosphate). The reaction sequence is CMP - CDP - dCDP -v dCMP ->dUMP- TMP (dTMP)- TDP (dTDP)- TTP (dITP). Methylation of dUMP to TMP is catalysed by th idylate synthase (EC 2.1.1.45). The cofiictor, AP,A/ -methylenetetrahydrofolic acid, transfers the active Cl unit to C5 of dUMP, and it also functions as a reducing agent in the formation of the methyl group from the active Cl unit. 

---