Ribose-5-phosphoric acid

D-ribose-5-phosphoric acid. C5H 04.H2P04. A constituent of nucleotides and nucleic acids. 

Initially, the Cj position of the ribose-5-phosphoric acid (ribose-5-phosphate) unit is activated by phosphorylation with ATP, and it becomes 5-phospho-D-ribosyl-l-pyrophosphoric acid (PRPP).This pyrophospho-ric acid unit is replaced with an activated ammonia derived from a glutamine with inversion of the stereoconfiguration at the Cj position. It is this nitrogen atom that subsequently becomes N-9 of the purine base. 

D-ribose, phosphoric acid, and four heterocyclic bases... 

Nucleic acids in which various purine and pyrimidine bases are united by bridges of D-2-deoxyribose or D-2-ribose phosphoric acid play vital roles in the metabolism of living cells.179 Many oligonucleotides (which are heterocyclic co-oligomers) have been synthesized in studying the biochemistry of nucleic acids.180... 

Co-enzym I, nicotinic amide-ribose-(phosphoric acid)2-ribose-adenine. 

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). 

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. 

Crystalline phosphoric acid has also been used to prepare sugar diphosphates, e.g. a-D-ribose 1,5-diphosphate (62) and hexose 1,6-diphosphates. 

Moderately simple syntheses have been performed for the purines cytosine and uracil but nothing seems to work as a prebiotic synthesis of the pyrimidines. Then adding the sugar ribose to the base makes them nucleosides and one phosphoric acid residue makes it a nucleotide, or specifically a mononucleotide a rare but curiously important sequence of events in present-day life but perhaps not for prebiotic chemistry and early life forms. 

Whilst many biochemicals are mono-esters of phosphoric acid, the nucleic acids DNA and RNA (see Section 14.2) provide us with good examples of diesters. A short portion of one strand of a DNA molecule is shown here the most significant difference in RNA is the use of ribose rather than deoxyribose as the sugar unit. 

The intermediate aminoacyl-AMP can also be seen to be an anhydride, but in this case a mixed anhydride of carboxylic and phosphoric acids (see Box 7.27). This can react with a hydroxyl group in ribose, part of... 

Each new double helix is comprised of one strand that was part of the original molecule and one strand that is newly synthesized. Not surprisingly, this is a very simplistic description of a quite complex process, catalysed by enzymes known as DNA polymerases. The precursors for synthesis of the new chain are the nucleoside triphosphates, dATP, dGTP, dTTP, and dCTP. We have already met ATP when we considered anhydrides of phosphoric acid (see Box 7.25) these compounds are analogues of ATP, though the sugar is deoxyribose rather than ribose. 

In standard conditions, the change in free enthalpy AG° (see p. 18) that occurs in the hydrolysis of phosphoric acid anhydride bonds amounts to -30 to -35 kj mol at pH 7. The particular anhydride bond of ATP that is cleaved only has a minor influence on AG° (1-2). Even the hydrolysis of diphosphate (also known as pyrophosphate 4) still yields more than -30 kJ mol . By contrast, cleavage of the ester bond between ribose and phosphate only provides -9 kJ mol (3). 

The DNA molecule is a double strand of nucleic acids, each consisting of a sequence of nucleosides, which are paired ribose sugar and phosphoric acid, held together in sequences of [—R(X)—P—], where X is one of four bases of thymine, cytosine, adenine, or guanine. Thymine can bond to adenine by two hydrogen bonds, and cytosine can bond to guanine by three hydrogen bonds. The two strands of DNA molecules run... 

Nucleotides are the phosphoric acid ester of nucleoside, while nucleosides are compounds in which nitrogenous bases (purines and pyrimidines) are conjugated to the pentose sugar (ribose or deoxyribose) by a b-glycosidic linkage. AMP, ATP, ADP, GMP, CMP, UMP are the examples of mononucleotides. 

Monosaccharides also form phosphate esters with phosphoric acid. Monosaccharide phosphate esters are important molecules in biological system. For example, in the DNA and RNA nucleotides, phosphate esters of 2-deoxyribose and ribose are present, respectively. Adenosine triphosphate (ATP), the triphosphate ester at C-5 of ribose in adenosine, is found extensively in living systems. 

Vitamin B12 consists of a porphyrin-like ring structure, with an atom of Co chelated at its centre, linked to a nucleotide base, ribose and phosphoric acid (6.34). A number of different groups can be attached to the free ligand site on the cobalt. Cyanocobalamin has -CN at this position and is the commercial and therapeutic form of the vitamin, although the principal dietary forms of B12 are 5 -deoxyadenosylcobalamin (with 5 -deoxyadeno-sine at the R position), methylcobalamin (-CH3) and hydroxocobalamin (-OH). Vitamin B12 acts as a co-factor for methionine synthetase and methylmalonyl CoA mutase. The former enzyme catalyses the transfer of the methyl group of 5-methyl-H4 folate to cobalamin and thence to homocysteine, forming methionine. Methylmalonyl CoA mutase catalyses the conversion of methylmalonyl CoA to succinyl CoA in the mitochondrion. 

An even more remarkable prediction was made by Crick and Watson (1953) of the structure of the vast molecules, such as that of deoxyribonucleic acid (DNA), which are concerned with the maintenance and transference of genetic information. These molecules contain very long chains of nucleotide units linked by covalency bonds. (A nucleotide consists of the residue of a sugar, often ribose or deoxyribose, one of a purine or pyrimidine base, and one of phosphoric acid, bonded together.) The Crick-Watson hypothesis was that the macromolecule consists of two such chains,... 

Some phosphoric acid derivatives of 2-desoxy-D-ribose have been obtained by enzymic methods of preparation. A reaction analogous to the phosphorolysis of glycogen to D-glucose 1-phosphate241 has been effected with either hypoxanthine- or guanine-D-riboside, both of which could be split by enzymic phosphorolysis with the formation of D-ribose 1-phosphate.242 The successful conclusion of these experiments prompted similar investigations with desoxyribonucleosides. 

The nucleic acids (Blackburn and Gait, 1995 Bloomfield et ah, 1999 Saenger, 1983), deoxyribonucleic acids (DNA), and ribonucleic acids (RNA) are polymers of nucleotides which are made up of three parts a purine or pyrimidine base, D-2-deoxyribose for DNA or D-ribose for RNA, and phosphoric acid. The nucleo-... 

Fig. 14.3. (a) The four organic bases present in DNA. Each base is attached to a ribose molecule through a bond from the nitrogen, (b) Structure of deoxyadenosine, a nucleotide formed from phosphoric acid, deoxyribose, and an organic base, adenine. (Reprinted from T. L. Brown and H. E. LeMay, Chemistry The Central Science, Prentice-Hall, 1977.)... 

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