Phosphate units

The biological transformations that involve ATP are both numerous and funda mental They include for example many phosphorylation reactions m which ATP trans fers one of its phosphate units to the —OH of another molecule These phosphoryla tions are catalyzed by enzymes called kinases An example is the first step m the metabolism of glucose... 

Nt = Typical nucleotide (phospate+sugar+base) O = Oeoxynbase sugar residue O = Phosphate unit... 

Schematic diagram of deoxyribonucleic acid (DNA) showing the pairing of nitrogen bases (A-T C-G) between parts of two strands of DNA, the backbone of each strand being composed of alternately linked sugar and phosphate units.

Figure 13-26. As the figure indicates, the backbone has directionality. Each phosphate unit forms a bridge from the 5 position of one ribose to the 3 position of another ribose.

Further condensation of phosphate groups leads to the polyphosphoric acids, which contain several phosphate units. The acids themselves are not particularly useful, but salts of some of these acids are used extensively. Triphosphoric acid, also known as tripolyphosphoric acid, H5P3O10, can be considered as a product of the reaction... 

The opportunity for tandem cyclization was explored. Here, the results can be accommodated by postulating the intermediacy of a vinyl radical [66]. For example, the controlled potential reduction of enol phosphate 246 affords 247 as a mixture of stereoisomers, in addition to a 15% yield of the linearly fused tricyclopentanoid 248. Assuming that the initial reduction cleaves the phosphate unit, then there exists the opportunity for the resulting radical 249 to be further reduced to afford a carbanion, or undergo a 5-exo-trig radical cyclization onto the pendant alkene. Given the nature of the products and the fact that they are inconsistent with the expectations of carbanion chemistry, it seems clear that the latter pathway dominates. 

Secondary structure of DNA consists of two strands of polynucleotides coiled around each there in the form of double helix. The backbone of each strand is sugar-phosphate unit and the base unit of each strand are pointed into the interior of the helix and are linked through H-bonds. G and C are held by three H-bonds, A and T are held by two bonds. Unlike DNA, RNA has a single strand. 

ATP Regarded as Store House of Energy Adenosine triphosphate (ATP) in a nucleotide consists of purine base adenine, a pentose sugar ribose and three molecules of phosphate. It contains two oxygen to phosphorus bonds between two phosphate units. These phosphorus bonds are called high energy phosphatic bonds. 

The sugar and phosphate groups form the backbone of a nucleic acid, and the amine bases exist as side chains. A nucleic acid can be thought of as alternating sugar-phosphate units with amine base projections ... 

In DNA and the related single-stranded RNA (ribonucleic acid), the phosphate units are monomeric and play a strictly structural role. Phosphates, however, are also essential to the metabolism of living cells, in which formation and subsequent hydrolysis of phosphate-phosphate bonds... 

The fact that twelve molybdate ions are bound to each phosphate unit in molybdophosphate has been exploited as an amplifying factor. The molybdophosphoric acid is extracted from the original solution into a mixture of diethyl ether or chloroform with butanol, in order to eliminate the excess of molybdate reagent it is then re-extracted into an aqueous phase and broken down with alkali. The molybdate ions are reacted with ammonium rhodanide90 or aminochlorobenzenethiol76 to give coloured products with absorption maxima at 470 and 710 nm, respectively. One phosphate ion thus yields twelve molybdate units, the optical absorbance is amplified with respect to that of the heteropoly phosphate complex and its measurement provides a sensitive determination procedure. 

A nucleoside contains a sugar and a base. A nucleotide also contains a phosphate 24.14 a chain o f nucleotides (deoxyribose and phosphate units)... 

When epinephrine occupies its receptor it activates the ligand binding/ G-protein/ adenylate cyclase cascade. This in turn phosphorylates the muscle enzyme, phosphorylase. This form of the enzyme is the active form which cleaves glucose 1-phosphate unit from glycogen, eventually depleting it... 

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