Nucleic acids purine bases

The bases are either monocyclic pyrimidines or bicyclic purines (see Section 14.1). Three pyrimidine bases are encountered in DNA and RNA, cytosine (C), thymine (T) and uracil (U). Cytosine is common to both DNA and RNA, but uracil is found only in RNA and thymine is found only in DNA. In the nucleic acid, the bases are linked through an A-glycoside bond to a sugar, either ribose or deoxyribose the combination base plus sugar is termed a nucleoside. The nitrogen bonded to the sugar is that shown. 

Purine bases IC. Computer programs for calculating the relative compositions of nucleotides, nucleic acids, purines. 

Adenosine was shown to be incorporated into nucleic acid purines, but to only about half the extent of adenine itself (L2). The incorporation of guanosine was also studied and here again the guanine derivative was a poorer precursor than the adenine derivative, but the utilization of guanosine was considerably greater than that of the aglycone (L22). The administration of the adenine nucleotides revealed that these compounds, whether as the 3 isomer or the 5 isomer, were poorer precursors than the free base adenine (Wl). With all nucleotides studied, the incorporation of the 5 isomer was less extensive than of the 3 isomer (R9). Roll et al. have shown that guanine nucleotides are considerably... 

The most important naturally occuring diazines are the pyrimidine bases uracil, thymine and cytosine, which are constituents of the nucleic acids (see 32.4). The nucleic acid pyrimidines are often drawn horizontally transposed from the representations used in this chapter, i.e. with N-3 to the north-west , mainly to draw attention to their structural similarity to the pyrimidine ring of the nucleic acid purines, which are traditionally drawn with the pyrimidine ring on the left. There are relatively few naturally occurring pyr-azines or pyridazines. 

Nucleic acids contain bases of two different types, pyrimidines and purines. The catabolism of the purines, adenine and guanine, produces uric acid. At physiological hydrogen ion concentration. uric acid is mostly ioni/ed and present in plasma as sodium urate (Fig. I). An elevated. serum urate concentration is known as hyperuricaemia. Uric acid and urate are relatively insoluble molecules which readily precipitate out of aqueous solutions such as urine or synovial fluid (Fig. 2). The consequence of this is the medical condition, gout. 

The coloured parts of the molecules below emphasize the characteristic features of the bases, purine bases in nucleic acids pyrimidine bases in nucleic acids... 

Bases of nucleic acids Nitrogenous bases (purines such as adenine and guanine or p3rrimidines such as cytosine, thymine, and uracil). Adenine, guanine, and c3rtosine are found in both deoxynucleotides and ribonucleotides, whereas uracil is found primarily in ribonucleotides, and th3miine in deoxynucleotides. 

The occurrence of methylated derivatives of purines in nucleic acids raises the question of their biological significance. It is possible that methylated purines were incorporated accidentally into nucleic acid and merely replaced natural bases because they were present in the cell for other purposes. The methylated purines may represent constituents of unknown coenzymes or may be vital components of some nucleic acid of specialized function. Also, the possibility should not be overlooked that the methylated purines were not useful to the organism, but represented minor by-products of the usual nucleic acid purines. However, an intriguing possibility has been offered that a methylated base might participate in the template coding of an uncommon amino acid such as cysteine or tryptophan or even act to produce a correct termination of the polypeptide chain 226). 

Nucleic acids are acidic substances present m the nuclei of cells and were known long before anyone suspected they were the primary substances involved m the storage transmission and processing of genetic information There are two kinds of nucleic acids ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) Both are complicated biopolymers based on three structural units a carbohydrate a phosphate ester linkage between carbohydrates and a heterocyclic aromatic compound The heterocyclic aro matic compounds are referred to as purine and pyrimidine bases We 11 begin with them and follow the structural thread... 

Purine and pyrimidine bases Nucleosides Nucleotides Nucleic acids... 

Two nitrogen containing heterocyclic aromatic compounds—pyrimidine and purine— are the parents of the bases that constitute a key structural unit of nucleic acids... 

Both pynmidme and purine are planar You will see how important this flat shape is when we consider the structure of nucleic acids In terms of their chemistry pyrimidine and purine resemble pyndme They are weak bases and relatively unreactive toward elec trophilic aromatic substitution... 

These relationships are general Hydroxyl substituted purines and pyrimidines exist in their keto forms ammo substituted ones retain structures with an ammo group on the ring The pyrimidine and punne bases m DNA and RNA listed m Table 28 1 follow this general rule Beginning m Section 28 7 we 11 see how critical it is that we know the cor rect tautomeric forms of the nucleic acid bases... 

Another property of pyrimidines and purines is their strong absorbance of ultraviolet (UV) light, which is also a consequence of the aromaticity of their heterocyclic ring structures. Figure 11.8 shows characteristic absorption spectra of several of the common bases of nucleic acids—adenine, uracil, cytosine, and guanine—in their nucleotide forms AMP, UMP, CMP, and GMP (see Section 11.4). This property is particularly useful in quantitative and qualitative analysis of nucleotides and nucleic acids. 

Aza Analogs of Pyrimidine and Purine Bases of Nucleic Acids... 

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. 

The 8-aza analogs of purine bases were the first to be studied among all the aza analogs of nucleic acid bases (as early as 1945). Before that time the chemistry of these substances had not been treated in detail from any aspect. Thus the entire chemistry of the u-triazolo [4,5-d]pyrimidines was developed only in connection with the study of antimetabolites of nucleic acid components. Therefore all the papers involved are largely of preparative character and only rarely discuss. theoretical points. 

Just as proteins are biopolymers made of amino acids, nucleic acids are biopolv-mers made of nucleotides joined together to form a long chain. Each nucleotide is composed of a nucleoside bonded to a phosphate group, and each nucleoside is composed of an aldopentose sugar linked through its anomeric carbon to the nitrogen atom of a heterocyclic purine or pyrimidine base. 

The nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are biological polymers that act as chemical carriers of an organism s genetic information. Enzyme-catalyzed hydrolysis of nucleic acids yields nucleotides, the monomer units from which RNA and DNA are constructed. Further enzyme-catalyzed hydrolysis of the nucleotides yields nucleosides plus phosphate. Nucleosides, in turn, consist of a purine or pyrimidine base linked to Cl of an aldopentose sugar—ribose in RNA and 2-deoxyribose in DNA. The nucleotides are joined by phosphate links between the 5 phosphate of one nucleotide and the 3 hydroxyl on the sugar of another nucleotide. 

Nucleotide (Section 28. ) A nucleic acid constituent, consisting of a sugar residue bonded both to a heterocyclic purine or pyrimidine base and to a phosphoric acid. 

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